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 $235.94   11.869%   $263.9437   $263.94   $263.95   $263.90  
  Purchase #2 $44.57   8.175%   $48.2136   $48.21   $48.20   $48.20  
  Purchase #3 $84.94   9.447%   $92.9643   $92.96   $92.95   $93.00  
  Purchase #4 $166.38   9.753%   $182.607   $182.61   $182.60   $182.60  
  Purchase #5 $161.31   9.271%   $176.2651   $176.27   $176.25   $176.30  
  Purchase #6 $143.65   12.184%   $161.1523   $161.15   $161.15   $161.20  
  Purchase #7 $56.37   8.679%   $61.2624   $61.26   $61.25   $61.30  
  7 purchase totals = $893.16       $986.4084   $986.40   $986.35   $986.50