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 $95.26   7.543%   $102.4455   $102.45   $102.45   $102.40  
  Purchase #2 $227.68   3.808%   $236.3501   $236.35   $236.35   $236.40  
  Purchase #3 $154.38   8.547%   $167.5749   $167.57   $167.55   $167.60  
  Purchase #4 $97.36   13.267%   $110.2768   $110.28   $110.30   $110.30  
  Purchase #5 $40.74   7.432%   $43.7678   $43.77   $43.75   $43.80  
  Purchase #6 $168.41   5.583%   $177.8123   $177.81   $177.80   $177.80  
  Purchase #7 $147.84   5.802%   $156.4177   $156.42   $156.40   $156.40  
  7 purchase totals = $931.67       $994.6451   $994.65   $994.60   $994.70