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 $10.67   6.828%   $11.3985   $11.40   $11.40   $11.40  
  Purchase #2 $241.48   10.298%   $266.3476   $266.35   $266.35   $266.30  
  Purchase #3 $54.47   7.201%   $58.3924   $58.39   $58.40   $58.40  
  Purchase #4 $227.39   10.560%   $251.4024   $251.40   $251.40   $251.40  
  Purchase #5 $13.72   3.309%   $14.174   $14.17   $14.15   $14.20  
  Purchase #6 $76.42   13.329%   $86.606   $86.61   $86.60   $86.60  
  Purchase #7 $165.88   8.152%   $179.4025   $179.40   $179.40   $179.40  
  7 purchase totals = $790.03       $867.7234   $867.72   $867.70   $867.70