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 $45.99   12.556%   $51.7645   $51.76   $51.75   $51.80  
  Purchase #2 $107.79   8.501%   $116.9532   $116.95   $116.95   $117.00  
  Purchase #3 $192.87   12.650%   $217.2681   $217.27   $217.25   $217.30  
  Purchase #4 $98.64   3.265%   $101.8606   $101.86   $101.85   $101.90  
  Purchase #5 $156.76   6.662%   $167.2034   $167.20   $167.20   $167.20  
  Purchase #6 $175.77   13.222%   $199.0103   $199.01   $199.00   $199.00  
  Purchase #7 $127.32   10.663%   $140.8961   $140.90   $140.90   $140.90  
  7 purchase totals = $905.14       $994.9562   $994.95   $994.90   $995.10