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 $215.94   13.822%   $245.7872   $245.79   $245.80   $245.80  
  Purchase #2 $211.89   3.664%   $219.6536   $219.65   $219.65   $219.70  
  Purchase #3 $95.38   4.610%   $99.777   $99.78   $99.80   $99.80  
  Purchase #4 $141.60   13.798%   $161.138   $161.14   $161.15   $161.10  
  Purchase #5 $58.33   10.574%   $64.4978   $64.50   $64.50   $64.50  
  Purchase #6 $89.84   6.566%   $95.7389   $95.74   $95.75   $95.70  
  Purchase #7 $41.44   6.874%   $44.2886   $44.29   $44.30   $44.30  
  7 purchase totals = $854.42       $930.8811   $930.89   $930.95   $930.90