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 $188.33   13.511%   $213.7753   $213.78   $213.80   $213.80  
  Purchase #2 $211.50   3.203%   $218.2743   $218.27   $218.25   $218.30  
  Purchase #3 $167.71   4.725%   $175.6343   $175.63   $175.65   $175.60  
  Purchase #4 $232.26   9.171%   $253.5606   $253.56   $253.55   $253.60  
  Purchase #5 $232.73   6.487%   $247.8272   $247.83   $247.85   $247.80  
  Purchase #6 $126.34   9.607%   $138.4775   $138.48   $138.50   $138.50  
  Purchase #7 $208.82   8.616%   $226.8119   $226.81   $226.80   $226.80  
  7 purchase totals = $1,367.69       $1,474.3611   $1,474.36   $1,474.40   $1,474.40