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 $206.83   10.258%   $228.0466   $228.05   $228.05   $228.00  
  Purchase #2 $193.31   4.154%   $201.3401   $201.34   $201.35   $201.30  
  Purchase #3 $43.51   11.526%   $48.525   $48.53   $48.55   $48.50  
  Purchase #4 $140.42   8.581%   $152.4694   $152.47   $152.45   $152.50  
  Purchase #5 $112.76   11.304%   $125.5064   $125.51   $125.50   $125.50  
  Purchase #6 $203.87   13.772%   $231.947   $231.95   $231.95   $231.90  
  Purchase #7 $245.34   5.490%   $258.8092   $258.81   $258.80   $258.80  
  7 purchase totals = $1,146.04       $1,246.6437   $1,246.66   $1,246.65   $1,246.50