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 $71.70   3.443%   $74.1686   $74.17   $74.15   $74.20  
  Purchase #2 $76.92   10.451%   $84.9589   $84.96   $84.95   $85.00  
  Purchase #3 $17.39   3.738%   $18.04   $18.04   $18.05   $18.00  
  Purchase #4 $233.35   5.166%   $245.4049   $245.40   $245.40   $245.40  
  Purchase #5 $156.68   4.140%   $163.1666   $163.17   $163.15   $163.20  
  Purchase #6 $160.63   4.658%   $168.1121   $168.11   $168.10   $168.10  
  Purchase #7 $6.62   9.336%   $7.238   $7.24   $7.25   $7.20  
  7 purchase totals = $723.29       $761.0891   $761.09   $761.05   $761.10