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 $67.40   3.781%   $69.9484   $69.95   $69.95   $69.90  
  Purchase #2 $218.99   3.158%   $225.9057   $225.91   $225.90   $225.90  
  Purchase #3 $110.76   5.194%   $116.5129   $116.51   $116.50   $116.50  
  Purchase #4 $155.35   5.394%   $163.7296   $163.73   $163.75   $163.70  
  Purchase #5 $209.54   12.726%   $236.2061   $236.21   $236.20   $236.20  
  Purchase #6 $57.40   8.449%   $62.2497   $62.25   $62.25   $62.20  
  Purchase #7 $118.41   12.148%   $132.7944   $132.79   $132.80   $132.80  
  7 purchase totals = $937.85       $1,007.3468   $1,007.35   $1,007.35   $1,007.20