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 $48.41   5.355%   $51.0024   $51.00   $51.00   $51.00  
  Purchase #2 $64.49   6.261%   $68.5277   $68.53   $68.55   $68.50  
  Purchase #3 $243.89   10.155%   $268.657   $268.66   $268.65   $268.70  
  Purchase #4 $135.60   5.856%   $143.5407   $143.54   $143.55   $143.50  
  Purchase #5 $121.94   3.332%   $126.003   $126.00   $126.00   $126.00  
  Purchase #6 $221.25   10.466%   $244.406   $244.41   $244.40   $244.40  
  Purchase #7 $86.94   7.542%   $93.497   $93.50   $93.50   $93.50  
  7 purchase totals = $922.52       $995.6338   $995.64   $995.65   $995.60