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 $222.35   11.518%   $247.9603   $247.96   $247.95   $248.00  
  Purchase #2 $194.91   12.339%   $218.9599   $218.96   $218.95   $219.00  
  Purchase #3 $170.69   7.289%   $183.1316   $183.13   $183.15   $183.10  
  Purchase #4 $94.56   3.324%   $97.7032   $97.70   $97.70   $97.70  
  Purchase #5 $83.37   5.784%   $88.1921   $88.19   $88.20   $88.20  
  Purchase #6 $12.64   8.591%   $13.7259   $13.73   $13.75   $13.70  
  Purchase #7 $151.77   7.428%   $163.0435   $163.04   $163.05   $163.00  
  7 purchase totals = $930.29       $1,012.7165   $1,012.71   $1,012.75   $1,012.70