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 $43.75   8.686%   $47.5501   $47.55   $47.55   $47.60  
  Purchase #2 $248.63   11.113%   $276.2603   $276.26   $276.25   $276.30  
  Purchase #3 $167.69   9.163%   $183.0554   $183.06   $183.05   $183.10  
  Purchase #4 $29.45   3.341%   $30.4339   $30.43   $30.45   $30.40  
  Purchase #5 $111.40   4.114%   $115.983   $115.98   $116.00   $116.00  
  Purchase #6 $180.52   9.310%   $197.3264   $197.33   $197.35   $197.30  
  Purchase #7 $132.75   7.746%   $143.0328   $143.03   $143.05   $143.00  
  7 purchase totals = $914.19       $993.6419   $993.64   $993.70   $993.70