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 $46.39   13.345%   $52.5807   $52.58   $52.60   $52.60  
  Purchase #2 $160.50   5.327%   $169.0498   $169.05   $169.05   $169.00  
  Purchase #3 $185.30   11.279%   $206.2   $206.20   $206.20   $206.20  
  Purchase #4 $38.68   13.139%   $43.7622   $43.76   $43.75   $43.80  
  Purchase #5 $195.58   3.740%   $202.8947   $202.89   $202.90   $202.90  
  Purchase #6 $102.55   10.280%   $113.0921   $113.09   $113.10   $113.10  
  Purchase #7 $112.84   11.114%   $125.381   $125.38   $125.40   $125.40  
  7 purchase totals = $841.84       $912.9605   $912.95   $913.00   $913.00