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 $54.54   7.168%   $58.4494   $58.45   $58.45   $58.40  
  Purchase #2 $169.33   3.379%   $175.0517   $175.05   $175.05   $175.10  
  Purchase #3 $161.26   13.261%   $182.6447   $182.64   $182.65   $182.60  
  Purchase #4 $52.29   12.533%   $58.8435   $58.84   $58.85   $58.80  
  Purchase #5 $87.74   8.647%   $95.3269   $95.33   $95.35   $95.30  
  Purchase #6 $151.94   10.453%   $167.8223   $167.82   $167.80   $167.80  
  Purchase #7 $123.43   7.611%   $132.8243   $132.82   $132.80   $132.80  
  7 purchase totals = $800.53       $870.9628   $870.95   $870.95   $870.80