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 $89.93   8.340%   $97.4302   $97.43   $97.45   $97.40  
  Purchase #2 $161.43   3.184%   $166.5699   $166.57   $166.55   $166.60  
  Purchase #3 $66.33   3.836%   $68.8744   $68.87   $68.85   $68.90  
  Purchase #4 $163.59   7.324%   $175.5713   $175.57   $175.55   $175.60  
  Purchase #5 $68.84   10.597%   $76.135   $76.14   $76.15   $76.10  
  Purchase #6 $54.89   5.657%   $57.9951   $58.00   $58.00   $58.00  
  Purchase #7 $167.84   8.646%   $182.3514   $182.35   $182.35   $182.40  
  7 purchase totals = $772.85       $824.9273   $824.93   $824.90   $825.00