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 $204.61   12.764%   $230.7264   $230.73   $230.75   $230.70  
  Purchase #2 $60.73   11.860%   $67.9326   $67.93   $67.95   $67.90  
  Purchase #3 $89.43   9.556%   $97.9759   $97.98   $98.00   $98.00  
  Purchase #4 $204.58   11.306%   $227.7098   $227.71   $227.70   $227.70  
  Purchase #5 $12.67   7.818%   $13.6605   $13.66   $13.65   $13.70  
  Purchase #6 $143.29   3.394%   $148.1533   $148.15   $148.15   $148.20  
  Purchase #7 $248.87   5.336%   $262.1497   $262.15   $262.15   $262.10  
  7 purchase totals = $964.18       $1,048.3082   $1,048.31   $1,048.35   $1,048.30