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 $48.51   13.470%   $55.0443   $55.04   $55.05   $55.00  
  Purchase #2 $240.75   13.813%   $274.0048   $274.00   $274.00   $274.00  
  Purchase #3 $181.34   3.201%   $187.1447   $187.14   $187.15   $187.10  
  Purchase #4 $69.46   12.618%   $78.2245   $78.22   $78.20   $78.20  
  Purchase #5 $105.92   13.786%   $120.5221   $120.52   $120.50   $120.50  
  Purchase #6 $180.75   7.322%   $193.9845   $193.98   $194.00   $194.00  
  Purchase #7 $51.55   8.457%   $55.9096   $55.91   $55.90   $55.90  
  7 purchase totals = $878.28       $964.8345   $964.81   $964.80   $964.70