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 $55.26   5.425%   $58.2579   $58.26   $58.25   $58.30  
  Purchase #2 $211.28   5.391%   $222.6701   $222.67   $222.65   $222.70  
  Purchase #3 $92.51   13.116%   $104.6436   $104.64   $104.65   $104.60  
  Purchase #4 $81.64   10.710%   $90.3836   $90.38   $90.40   $90.40  
  Purchase #5 $224.85   11.772%   $251.3193   $251.32   $251.30   $251.30  
  Purchase #6 $64.60   5.291%   $68.018   $68.02   $68.00   $68.00  
  Purchase #7 $180.57   11.449%   $201.2435   $201.24   $201.25   $201.20  
  7 purchase totals = $910.71       $996.5360   $996.53   $996.50   $996.50