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 $49.51   7.856%   $53.3995   $53.40   $53.40   $53.40  
  Purchase #2 $117.59   7.136%   $125.9812   $125.98   $126.00   $126.00  
  Purchase #3 $207.95   9.220%   $227.123   $227.12   $227.10   $227.10  
  Purchase #4 $80.98   5.545%   $85.4703   $85.47   $85.45   $85.50  
  Purchase #5 $196.34   6.378%   $208.8626   $208.86   $208.85   $208.90  
  Purchase #6 $125.45   10.726%   $138.9058   $138.91   $138.90   $138.90  
  Purchase #7 $19.94   11.544%   $22.2419   $22.24   $22.25   $22.20  
  7 purchase totals = $797.76       $861.9843   $861.98   $861.95   $862.00