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 $31.64   6.278%   $33.6264   $33.63   $33.65   $33.60  
  Purchase #2 $122.61   12.824%   $138.3335   $138.33   $138.35   $138.30  
  Purchase #3 $102.40   12.407%   $115.1048   $115.10   $115.10   $115.10  
  Purchase #4 $244.54   5.635%   $258.3198   $258.32   $258.30   $258.30  
  Purchase #5 $239.47   8.863%   $260.6942   $260.69   $260.70   $260.70  
  Purchase #6 $131.74   12.349%   $148.0086   $148.01   $148.00   $148.00  
  Purchase #7 $11.84   13.225%   $13.4058   $13.41   $13.40   $13.40  
  7 purchase totals = $884.24       $967.4931   $967.49   $967.50   $967.40