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 $45.84   9.129%   $50.0247   $50.02   $50.00   $50.00  
  Purchase #2 $170.66   13.717%   $194.0694   $194.07   $194.05   $194.10  
  Purchase #3 $112.78   6.120%   $119.6821   $119.68   $119.70   $119.70  
  Purchase #4 $201.28   7.812%   $217.004   $217.00   $217.00   $217.00  
  Purchase #5 $93.68   10.236%   $103.2691   $103.27   $103.25   $103.30  
  Purchase #6 $185.53   9.242%   $202.6767   $202.68   $202.70   $202.70  
  Purchase #7 $65.82   3.113%   $67.869   $67.87   $67.85   $67.90  
  7 purchase totals = $875.59       $954.5950   $954.59   $954.55   $954.70