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 $235.52   8.252%   $254.9551   $254.96   $254.95   $255.00  
  Purchase #2 $234.38   7.213%   $251.2858   $251.29   $251.30   $251.30  
  Purchase #3 $243.56   7.853%   $262.6868   $262.69   $262.70   $262.70  
  Purchase #4 $232.60   7.788%   $250.7149   $250.71   $250.70   $250.70  
  Purchase #5 $174.72   5.622%   $184.5428   $184.54   $184.55   $184.50  
  Purchase #6 $184.44   5.830%   $195.1929   $195.19   $195.20   $195.20  
  Purchase #7 $86.98   10.252%   $95.8972   $95.90   $95.90   $95.90  
  7 purchase totals = $1,392.20       $1,495.2755   $1,495.28   $1,495.30   $1,495.30