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 $58.54   13.774%   $66.6033   $66.60   $66.60   $66.60  
  Purchase #2 $114.94   8.603%   $124.8283   $124.83   $124.85   $124.80  
  Purchase #3 $161.87   7.387%   $173.8273   $173.83   $173.85   $173.80  
  Purchase #4 $53.30   10.350%   $58.8166   $58.82   $58.80   $58.80  
  Purchase #5 $97.85   5.123%   $102.8629   $102.86   $102.85   $102.90  
  Purchase #6 $151.65   5.709%   $160.3077   $160.31   $160.30   $160.30  
  Purchase #7 $202.85   11.836%   $226.8593   $226.86   $226.85   $226.90  
  7 purchase totals = $841.00       $914.1054   $914.11   $914.10   $914.10