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 $68.41   13.180%   $77.4264   $77.43   $77.45   $77.40  
  Purchase #2 $149.65   7.792%   $161.3107   $161.31   $161.30   $161.30  
  Purchase #3 $84.42   10.624%   $93.3888   $93.39   $93.40   $93.40  
  Purchase #4 $99.93   3.245%   $103.1727   $103.17   $103.15   $103.20  
  Purchase #5 $222.57   7.618%   $239.5254   $239.53   $239.55   $239.50  
  Purchase #6 $43.97   9.162%   $47.9985   $48.00   $48.00   $48.00  
  Purchase #7 $66.25   7.190%   $71.0134   $71.01   $71.00   $71.00  
  7 purchase totals = $735.20       $793.8359   $793.84   $793.85   $793.80