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 $124.99   8.128%   $135.1492   $135.15   $135.15   $135.10  
  Purchase #2 $64.54   13.660%   $73.3562   $73.36   $73.35   $73.40  
  Purchase #3 $25.92   4.242%   $27.0195   $27.02   $27.00   $27.00  
  Purchase #4 $209.73   13.182%   $237.3766   $237.38   $237.40   $237.40  
  Purchase #5 $58.60   7.210%   $62.8251   $62.83   $62.85   $62.80  
  Purchase #6 $155.90   8.381%   $168.966   $168.97   $168.95   $169.00  
  Purchase #7 $41.90   6.245%   $44.5167   $44.52   $44.50   $44.50  
  7 purchase totals = $681.58       $749.2093   $749.23   $749.20   $749.20