Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.86   7.714%   $123.7203   $123.72   $123.70   $123.70  
  Purchase #2 $213.79   10.397%   $236.0177   $236.02   $236.00   $236.00  
  Purchase #3 $233.56   11.688%   $260.8585   $260.86   $260.85   $260.90  
  Purchase #4 $221.74   3.213%   $228.8645   $228.86   $228.85   $228.90  
  Purchase #5 $217.61   11.426%   $242.4741   $242.47   $242.45   $242.50  
  Purchase #6 $164.45   9.143%   $179.4857   $179.49   $179.50   $179.50  
  Purchase #7 $170.94   7.811%   $184.2921   $184.29   $184.30   $184.30  
  7 purchase totals = $1,336.95       $1,455.7129   $1,455.71   $1,455.65   $1,455.80