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 $191.75   11.611%   $214.0141   $214.01   $214.00   $214.00  
  Purchase #2 $67.63   13.665%   $76.8716   $76.87   $76.85   $76.90  
  Purchase #3 $208.46   10.659%   $230.6798   $230.68   $230.70   $230.70  
  Purchase #4 $146.63   11.272%   $163.1581   $163.16   $163.15   $163.20  
  Purchase #5 $45.43   8.548%   $49.3134   $49.31   $49.30   $49.30  
  Purchase #6 $232.62   3.493%   $240.7454   $240.75   $240.75   $240.70  
  Purchase #7 $69.36   9.226%   $75.7592   $75.76   $75.75   $75.80  
  7 purchase totals = $961.88       $1,050.5416   $1,050.54   $1,050.50   $1,050.60