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 $67.98   9.820%   $74.6556   $74.66   $74.65   $74.70  
  Purchase #2 $249.38   12.278%   $279.9989   $280.00   $280.00   $280.00  
  Purchase #3 $50.68   11.429%   $56.4722   $56.47   $56.45   $56.50  
  Purchase #4 $241.71   10.457%   $266.9856   $266.99   $267.00   $267.00  
  Purchase #5 $69.51   13.626%   $78.9814   $78.98   $79.00   $79.00  
  Purchase #6 $117.40   11.492%   $130.8916   $130.89   $130.90   $130.90  
  Purchase #7 $173.91   12.193%   $195.1148   $195.11   $195.10   $195.10  
  7 purchase totals = $970.57       $1,083.1001   $1,083.10   $1,083.10   $1,083.20