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 $96.30   8.193%   $104.1899   $104.19   $104.20   $104.20  
  Purchase #2 $100.71   5.682%   $106.4323   $106.43   $106.45   $106.40  
  Purchase #3 $246.92   5.292%   $259.987   $259.99   $260.00   $260.00  
  Purchase #4 $54.81   12.150%   $61.4694   $61.47   $61.45   $61.50  
  Purchase #5 $58.59   7.790%   $63.1542   $63.15   $63.15   $63.20  
  Purchase #6 $237.73   9.431%   $260.1503   $260.15   $260.15   $260.20  
  Purchase #7 $10.84   13.724%   $12.3277   $12.33   $12.35   $12.30  
  7 purchase totals = $805.90       $867.7108   $867.71   $867.75   $867.80