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 $63.82   5.424%   $67.2816   $67.28   $67.30   $67.30  
  Purchase #2 $239.26   9.402%   $261.7552   $261.76   $261.75   $261.80  
  Purchase #3 $155.95   8.445%   $169.12   $169.12   $169.10   $169.10  
  Purchase #4 $238.45   6.199%   $253.2315   $253.23   $253.25   $253.20  
  Purchase #5 $19.83   3.265%   $20.4774   $20.48   $20.50   $20.50  
  Purchase #6 $141.84   7.366%   $152.2879   $152.29   $152.30   $152.30  
  Purchase #7 $60.37   13.339%   $68.4228   $68.42   $68.40   $68.40  
  7 purchase totals = $919.52       $992.5764   $992.58   $992.60   $992.60