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 $76.46   9.324%   $83.5891   $83.59   $83.60   $83.60  
  Purchase #2 $195.31   7.682%   $210.3137   $210.31   $210.30   $210.30  
  Purchase #3 $232.96   13.544%   $264.5121   $264.51   $264.50   $264.50  
  Purchase #4 $169.49   3.824%   $175.9713   $175.97   $175.95   $176.00  
  Purchase #5 $178.99   6.209%   $190.1035   $190.10   $190.10   $190.10  
  Purchase #6 $193.50   7.292%   $207.61   $207.61   $207.60   $207.60  
  Purchase #7 $92.86   12.642%   $104.5994   $104.60   $104.60   $104.60  
  7 purchase totals = $1,139.57       $1,236.6991   $1,236.69   $1,236.65   $1,236.70