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 $218.50   8.721%   $237.5554   $237.56   $237.55   $237.60  
  Purchase #2 $68.27   12.251%   $76.6338   $76.63   $76.65   $76.60  
  Purchase #3 $148.58   5.608%   $156.9124   $156.91   $156.90   $156.90  
  Purchase #4 $86.35   3.410%   $89.2945   $89.29   $89.30   $89.30  
  Purchase #5 $47.64   5.585%   $50.3007   $50.30   $50.30   $50.30  
  Purchase #6 $97.57   5.220%   $102.6632   $102.66   $102.65   $102.70  
  Purchase #7 $209.42   3.491%   $216.7309   $216.73   $216.75   $216.70  
  7 purchase totals = $876.33       $930.0909   $930.08   $930.10   $930.10