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 $61.26   4.139%   $63.7956   $63.80   $63.80   $63.80  
  Purchase #2 $194.27   11.697%   $216.9938   $216.99   $217.00   $217.00  
  Purchase #3 $178.78   11.809%   $199.8921   $199.89   $199.90   $199.90  
  Purchase #4 $75.82   5.858%   $80.2615   $80.26   $80.25   $80.30  
  Purchase #5 $118.72   13.663%   $134.9407   $134.94   $134.95   $134.90  
  Purchase #6 $15.43   8.491%   $16.7402   $16.74   $16.75   $16.70  
  Purchase #7 $62.54   12.649%   $70.4507   $70.45   $70.45   $70.50  
  7 purchase totals = $706.82       $783.0746   $783.07   $783.10   $783.10