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 $176.43   11.809%   $197.2646   $197.26   $197.25   $197.30  
  Purchase #2 $131.67   10.725%   $145.7916   $145.79   $145.80   $145.80  
  Purchase #3 $55.42   4.183%   $57.7382   $57.74   $57.75   $57.70  
  Purchase #4 $192.73   9.216%   $210.492   $210.49   $210.50   $210.50  
  Purchase #5 $207.48   4.533%   $216.8851   $216.89   $216.90   $216.90  
  Purchase #6 $25.93   12.346%   $29.1313   $29.13   $29.15   $29.10  
  Purchase #7 $83.66   10.152%   $92.1532   $92.15   $92.15   $92.20  
  7 purchase totals = $873.32       $949.4560   $949.45   $949.50   $949.50