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 $84.86   4.235%   $88.4538   $88.45   $88.45   $88.50  
  Purchase #2 $172.43   12.299%   $193.6372   $193.64   $193.65   $193.60  
  Purchase #3 $196.57   6.575%   $209.4945   $209.49   $209.50   $209.50  
  Purchase #4 $167.45   4.829%   $175.5362   $175.54   $175.55   $175.50  
  Purchase #5 $131.71   11.353%   $146.663   $146.66   $146.65   $146.70  
  Purchase #6 $69.30   12.516%   $77.9736   $77.97   $77.95   $78.00  
  Purchase #7 $236.90   7.117%   $253.7602   $253.76   $253.75   $253.80  
  7 purchase totals = $1,059.22       $1,145.5185   $1,145.51   $1,145.50   $1,145.60