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 $148.91   11.594%   $166.1746   $166.17   $166.15   $166.20  
  Purchase #2 $148.69   8.158%   $160.8201   $160.82   $160.80   $160.80  
  Purchase #3 $247.88   7.509%   $266.4933   $266.49   $266.50   $266.50  
  Purchase #4 $112.72   11.792%   $126.0119   $126.01   $126.00   $126.00  
  Purchase #5 $118.25   11.591%   $131.9564   $131.96   $131.95   $132.00  
  Purchase #6 $69.57   5.128%   $73.1375   $73.14   $73.15   $73.10  
  Purchase #7 $59.44   5.547%   $62.7371   $62.74   $62.75   $62.70  
  7 purchase totals = $905.46       $987.3309   $987.33   $987.30   $987.30