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 $220.95   10.222%   $243.5355   $243.54   $243.55   $243.50  
  Purchase #2 $44.46   7.860%   $47.9546   $47.95   $47.95   $48.00  
  Purchase #3 $109.38   8.403%   $118.5712   $118.57   $118.55   $118.60  
  Purchase #4 $50.91   13.588%   $57.8277   $57.83   $57.85   $57.80  
  Purchase #5 $141.66   13.428%   $160.6821   $160.68   $160.70   $160.70  
  Purchase #6 $90.52   3.834%   $93.9905   $93.99   $94.00   $94.00  
  Purchase #7 $215.76   6.547%   $229.8858   $229.89   $229.90   $229.90  
  7 purchase totals = $873.64       $952.4474   $952.45   $952.50   $952.50