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 $48.94   7.869%   $52.7911   $52.79   $52.80   $52.80  
  Purchase #2 $208.97   12.407%   $234.8969   $234.90   $234.90   $234.90  
  Purchase #3 $244.47   5.669%   $258.329   $258.33   $258.35   $258.30  
  Purchase #4 $106.41   5.369%   $112.1232   $112.12   $112.10   $112.10  
  Purchase #5 $103.83   12.641%   $116.9552   $116.96   $116.95   $117.00  
  Purchase #6 $163.83   12.281%   $183.95   $183.95   $183.95   $184.00  
  Purchase #7 $166.46   5.863%   $176.2195   $176.22   $176.20   $176.20  
  7 purchase totals = $1,042.91       $1,135.2649   $1,135.27   $1,135.25   $1,135.30