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 $70.61   4.140%   $73.5333   $73.53   $73.55   $73.50  
  Purchase #2 $67.71   12.534%   $76.1968   $76.20   $76.20   $76.20  
  Purchase #3 $192.62   6.458%   $205.0594   $205.06   $205.05   $205.10  
  Purchase #4 $199.97   8.571%   $217.1094   $217.11   $217.10   $217.10  
  Purchase #5 $147.54   12.471%   $165.9397   $165.94   $165.95   $165.90  
  Purchase #6 $78.35   6.312%   $83.2955   $83.30   $83.30   $83.30  
  Purchase #7 $177.54   7.131%   $190.2004   $190.20   $190.20   $190.20  
  7 purchase totals = $934.34       $1,011.3345   $1,011.34   $1,011.35   $1,011.30