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 $83.67   11.538%   $93.3238   $93.32   $93.30   $93.30  
  Purchase #2 $32.83   13.501%   $37.2624   $37.26   $37.25   $37.30  
  Purchase #3 $130.44   10.691%   $144.3853   $144.39   $144.40   $144.40  
  Purchase #4 $187.91   10.795%   $208.1949   $208.19   $208.20   $208.20  
  Purchase #5 $147.60   7.391%   $158.5091   $158.51   $158.50   $158.50  
  Purchase #6 $97.92   9.103%   $106.8337   $106.83   $106.85   $106.80  
  Purchase #7 $88.71   10.296%   $97.8436   $97.84   $97.85   $97.80  
  7 purchase totals = $769.08       $846.3528   $846.34   $846.35   $846.30