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 $10.46   8.873%   $11.3881   $11.39   $11.40   $11.40  
  Purchase #2 $118.62   11.370%   $132.1071   $132.11   $132.10   $132.10  
  Purchase #3 $102.55   4.293%   $106.9525   $106.95   $106.95   $107.00  
  Purchase #4 $66.91   7.412%   $71.8694   $71.87   $71.85   $71.90  
  Purchase #5 $232.64   11.493%   $259.3773   $259.38   $259.40   $259.40  
  Purchase #6 $41.26   13.559%   $46.8544   $46.85   $46.85   $46.90  
  Purchase #7 $125.73   6.801%   $134.2809   $134.28   $134.30   $134.30  
  7 purchase totals = $698.17       $762.8297   $762.83   $762.85   $763.00