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 $50.38   10.623%   $55.7319   $55.73   $55.75   $55.70  
  Purchase #2 $34.74   5.617%   $36.6913   $36.69   $36.70   $36.70  
  Purchase #3 $232.77   3.746%   $241.4896   $241.49   $241.50   $241.50  
  Purchase #4 $93.70   11.700%   $104.6629   $104.66   $104.65   $104.70  
  Purchase #5 $49.90   7.623%   $53.7039   $53.70   $53.70   $53.70  
  Purchase #6 $190.52   4.872%   $199.8021   $199.80   $199.80   $199.80  
  Purchase #7 $233.79   11.547%   $260.7857   $260.79   $260.80   $260.80  
  7 purchase totals = $885.80       $952.8674   $952.86   $952.90   $952.90