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 $64.83   6.202%   $68.8508   $68.85   $68.85   $68.90  
  Purchase #2 $225.43   5.704%   $238.2885   $238.29   $238.30   $238.30  
  Purchase #3 $178.40   4.583%   $186.5761   $186.58   $186.60   $186.60  
  Purchase #4 $220.39   8.854%   $239.9033   $239.90   $239.90   $239.90  
  Purchase #5 $67.45   12.601%   $75.9494   $75.95   $75.95   $75.90  
  Purchase #6 $58.62   4.516%   $61.2673   $61.27   $61.25   $61.30  
  Purchase #7 $97.83   4.855%   $102.5796   $102.58   $102.60   $102.60  
  7 purchase totals = $912.95       $973.4150   $973.42   $973.45   $973.50