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 $87.97   5.462%   $92.7749   $92.77   $92.75   $92.80  
  Purchase #2 $221.39   9.453%   $242.318   $242.32   $242.30   $242.30  
  Purchase #3 $203.61   5.171%   $214.1387   $214.14   $214.15   $214.10  
  Purchase #4 $82.79   10.220%   $91.2511   $91.25   $91.25   $91.30  
  Purchase #5 $46.43   11.768%   $51.8939   $51.89   $51.90   $51.90  
  Purchase #6 $136.63   7.610%   $147.0275   $147.03   $147.05   $147.00  
  Purchase #7 $173.54   5.190%   $182.5467   $182.55   $182.55   $182.50  
  7 purchase totals = $952.36       $1,021.9508   $1,021.95   $1,021.95   $1,021.90