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 $209.85   8.261%   $227.1857   $227.19   $227.20   $227.20  
  Purchase #2 $236.33   10.765%   $261.7709   $261.77   $261.75   $261.80  
  Purchase #3 $52.67   8.146%   $56.9605   $56.96   $56.95   $57.00  
  Purchase #4 $227.58   10.676%   $251.8764   $251.88   $251.90   $251.90  
  Purchase #5 $160.46   9.707%   $176.0359   $176.04   $176.05   $176.00  
  Purchase #6 $234.96   8.242%   $254.3254   $254.33   $254.35   $254.30  
  Purchase #7 $144.88   6.421%   $154.1827   $154.18   $154.20   $154.20  
  7 purchase totals = $1,266.73       $1,382.3375   $1,382.35   $1,382.40   $1,382.40