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 $178.82   11.706%   $199.7527   $199.75   $199.75   $199.80  
  Purchase #2 $201.59   11.272%   $224.3132   $224.31   $224.30   $224.30  
  Purchase #3 $59.39   6.493%   $63.2462   $63.25   $63.25   $63.20  
  Purchase #4 $47.60   11.759%   $53.1973   $53.20   $53.20   $53.20  
  Purchase #5 $129.98   3.599%   $134.658   $134.66   $134.65   $134.70  
  Purchase #6 $78.54   8.826%   $85.4719   $85.47   $85.45   $85.50  
  Purchase #7 $76.62   12.667%   $86.3255   $86.33   $86.35   $86.30  
  7 purchase totals = $772.54       $846.9648   $846.97   $846.95   $847.00