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 $71.49   9.531%   $78.3037   $78.30   $78.30   $78.30  
  Purchase #2 $194.72   5.792%   $205.9982   $206.00   $206.00   $206.00  
  Purchase #3 $193.96   8.577%   $210.5959   $210.60   $210.60   $210.60  
  Purchase #4 $185.67   8.668%   $201.7639   $201.76   $201.75   $201.80  
  Purchase #5 $207.87   8.381%   $225.2916   $225.29   $225.30   $225.30  
  Purchase #6 $249.40   11.619%   $278.3778   $278.38   $278.40   $278.40  
  Purchase #7 $101.92   11.354%   $113.492   $113.49   $113.50   $113.50  
  7 purchase totals = $1,205.03       $1,313.8231   $1,313.82   $1,313.85   $1,313.90