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 $53.48   10.196%   $58.9328   $58.93   $58.95   $58.90  
  Purchase #2 $183.63   8.429%   $199.1082   $199.11   $199.10   $199.10  
  Purchase #3 $97.39   4.559%   $101.83   $101.83   $101.85   $101.80  
  Purchase #4 $248.98   13.634%   $282.9259   $282.93   $282.95   $282.90  
  Purchase #5 $63.97   7.232%   $68.5963   $68.60   $68.60   $68.60  
  Purchase #6 $39.92   4.134%   $41.5703   $41.57   $41.55   $41.60  
  Purchase #7 $121.33   6.145%   $128.7857   $128.79   $128.80   $128.80  
  7 purchase totals = $808.70       $881.7492   $881.76   $881.80   $881.70