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 $32.65   8.811%   $35.5268   $35.53   $35.55   $35.50  
  Purchase #2 $65.69   4.870%   $68.8891   $68.89   $68.90   $68.90  
  Purchase #3 $38.73   10.237%   $42.6948   $42.69   $42.70   $42.70  
  Purchase #4 $84.96   11.781%   $94.9691   $94.97   $94.95   $95.00  
  Purchase #5 $161.26   6.621%   $171.937   $171.94   $171.95   $171.90  
  Purchase #6 $166.33   8.698%   $180.7974   $180.80   $180.80   $180.80  
  Purchase #7 $136.81   12.319%   $153.6636   $153.66   $153.65   $153.70  
  7 purchase totals = $686.43       $748.4778   $748.48   $748.50   $748.50