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 $65.78   4.669%   $68.8513   $68.85   $68.85   $68.90  
  Purchase #2 $24.32   7.406%   $26.1211   $26.12   $26.10   $26.10  
  Purchase #3 $231.28   6.559%   $246.4497   $246.45   $246.45   $246.40  
  Purchase #4 $153.95   10.134%   $169.5513   $169.55   $169.55   $169.60  
  Purchase #5 $110.55   13.424%   $125.3902   $125.39   $125.40   $125.40  
  Purchase #6 $58.59   3.417%   $60.592   $60.59   $60.60   $60.60  
  Purchase #7 $192.92   8.694%   $209.6925   $209.69   $209.70   $209.70  
  7 purchase totals = $837.39       $906.6481   $906.64   $906.65   $906.70