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 $244.59   8.464%   $265.2921   $265.29   $265.30   $265.30  
  Purchase #2 $218.93   12.673%   $246.675   $246.68   $246.70   $246.70  
  Purchase #3 $123.41   7.283%   $132.398   $132.40   $132.40   $132.40  
  Purchase #4 $178.42   9.478%   $195.3306   $195.33   $195.35   $195.30  
  Purchase #5 $66.69   9.251%   $72.8595   $72.86   $72.85   $72.90  
  Purchase #6 $127.43   12.268%   $143.0631   $143.06   $143.05   $143.10  
  Purchase #7 $230.26   6.613%   $245.4871   $245.49   $245.50   $245.50  
  7 purchase totals = $1,189.73       $1,301.1054   $1,301.11   $1,301.15   $1,301.20