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 $119.82   12.804%   $135.1618   $135.16   $135.15   $135.20  
  Purchase #2 $137.41   13.500%   $155.9604   $155.96   $155.95   $156.00  
  Purchase #3 $179.90   13.120%   $203.5029   $203.50   $203.50   $203.50  
  Purchase #4 $30.26   5.139%   $31.8151   $31.82   $31.80   $31.80  
  Purchase #5 $245.73   12.589%   $276.6649   $276.66   $276.65   $276.70  
  Purchase #6 $83.53   10.514%   $92.3123   $92.31   $92.30   $92.30  
  Purchase #7 $36.90   4.710%   $38.638   $38.64   $38.65   $38.60  
  7 purchase totals = $833.55       $934.0554   $934.05   $934.00   $934.10