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 $43.58   8.459%   $47.2664   $47.27   $47.25   $47.30  
  Purchase #2 $201.80   9.567%   $221.1062   $221.11   $221.10   $221.10  
  Purchase #3 $108.51   7.660%   $116.8219   $116.82   $116.80   $116.80  
  Purchase #4 $13.95   11.834%   $15.6008   $15.60   $15.60   $15.60  
  Purchase #5 $137.30   3.406%   $141.9764   $141.98   $142.00   $142.00  
  Purchase #6 $59.50   3.527%   $61.5986   $61.60   $61.60   $61.60  
  Purchase #7 $156.55   9.870%   $172.0015   $172.00   $172.00   $172.00  
  7 purchase totals = $721.19       $776.3718   $776.38   $776.35   $776.40