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 $44.93   4.413%   $46.9128   $46.91   $46.90   $46.90  
  Purchase #2 $117.57   7.129%   $125.9516   $125.95   $125.95   $126.00  
  Purchase #3 $24.76   4.636%   $25.9079   $25.91   $25.90   $25.90  
  Purchase #4 $176.67   9.706%   $193.8176   $193.82   $193.80   $193.80  
  Purchase #5 $19.77   11.222%   $21.9886   $21.99   $22.00   $22.00  
  Purchase #6 $248.88   8.829%   $270.8536   $270.85   $270.85   $270.90  
  Purchase #7 $241.77   13.183%   $273.6425   $273.64   $273.65   $273.60  
  7 purchase totals = $874.35       $959.0746   $959.07   $959.05   $959.10