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 $237.89   5.398%   $250.7313   $250.73   $250.75   $250.70  
  Purchase #2 $101.25   9.314%   $110.6804   $110.68   $110.70   $110.70  
  Purchase #3 $113.78   4.434%   $118.825   $118.83   $118.85   $118.80  
  Purchase #4 $151.29   5.422%   $159.4929   $159.49   $159.50   $159.50  
  Purchase #5 $57.85   8.463%   $62.7458   $62.75   $62.75   $62.70  
  Purchase #6 $147.80   4.174%   $153.9692   $153.97   $153.95   $154.00  
  Purchase #7 $182.57   13.762%   $207.6953   $207.70   $207.70   $207.70  
  7 purchase totals = $992.43       $1,064.1399   $1,064.15   $1,064.20   $1,064.10