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 $118.96   5.622%   $125.6479   $125.65   $125.65   $125.60  
  Purchase #2 $16.59   7.239%   $17.791   $17.79   $17.80   $17.80  
  Purchase #3 $136.74   11.554%   $152.5389   $152.54   $152.55   $152.50  
  Purchase #4 $209.66   3.378%   $216.7423   $216.74   $216.75   $216.70  
  Purchase #5 $184.52   4.548%   $192.912   $192.91   $192.90   $192.90  
  Purchase #6 $70.56   7.304%   $75.7137   $75.71   $75.70   $75.70  
  Purchase #7 $201.80   4.191%   $210.2574   $210.26   $210.25   $210.30  
  7 purchase totals = $938.83       $991.6032   $991.60   $991.60   $991.50