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 $209.95   10.459%   $231.9087   $231.91   $231.90   $231.90  
  Purchase #2 $161.42   9.159%   $176.2045   $176.20   $176.20   $176.20  
  Purchase #3 $105.88   4.256%   $110.3863   $110.39   $110.40   $110.40  
  Purchase #4 $112.35   5.519%   $118.5506   $118.55   $118.55   $118.60  
  Purchase #5 $97.27   12.279%   $109.2138   $109.21   $109.20   $109.20  
  Purchase #6 $132.49   10.533%   $146.4452   $146.45   $146.45   $146.40  
  Purchase #7 $130.93   7.519%   $140.7746   $140.77   $140.75   $140.80  
  7 purchase totals = $950.29       $1,033.4837   $1,033.48   $1,033.45   $1,033.50