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 $141.86   8.520%   $153.9465   $153.95   $153.95   $153.90  
  Purchase #2 $232.59   13.631%   $264.2943   $264.29   $264.30   $264.30  
  Purchase #3 $119.51   12.503%   $134.4523   $134.45   $134.45   $134.50  
  Purchase #4 $95.95   9.301%   $104.8743   $104.87   $104.85   $104.90  
  Purchase #5 $21.71   9.510%   $23.7746   $23.77   $23.75   $23.80  
  Purchase #6 $126.48   3.448%   $130.841   $130.84   $130.85   $130.80  
  Purchase #7 $201.98   6.836%   $215.7874   $215.79   $215.80   $215.80  
  7 purchase totals = $940.08       $1,027.9704   $1,027.96   $1,027.95   $1,028.00