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 $210.28   8.726%   $228.629   $228.63   $228.65   $228.60  
  Purchase #2 $50.73   4.156%   $52.8383   $52.84   $52.85   $52.80  
  Purchase #3 $97.41   4.230%   $101.5304   $101.53   $101.55   $101.50  
  Purchase #4 $169.66   7.529%   $182.4337   $182.43   $182.45   $182.40  
  Purchase #5 $43.41   10.124%   $47.8048   $47.80   $47.80   $47.80  
  Purchase #6 $214.48   10.459%   $236.9125   $236.91   $236.90   $236.90  
  Purchase #7 $62.71   3.386%   $64.8334   $64.83   $64.85   $64.80  
  7 purchase totals = $848.68       $914.9821   $914.97   $915.05   $914.80