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 $104.25   8.379%   $112.9851   $112.99   $113.00   $113.00  
  Purchase #2 $30.45   11.122%   $33.8366   $33.84   $33.85   $33.80  
  Purchase #3 $101.51   4.581%   $106.1602   $106.16   $106.15   $106.20  
  Purchase #4 $27.30   3.782%   $28.3325   $28.33   $28.35   $28.30  
  Purchase #5 $194.98   9.322%   $213.156   $213.16   $213.15   $213.20  
  Purchase #6 $208.84   11.659%   $233.1887   $233.19   $233.20   $233.20  
  Purchase #7 $230.36   4.361%   $240.406   $240.41   $240.40   $240.40  
  7 purchase totals = $897.69       $968.0651   $968.08   $968.10   $968.10