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 $245.29   9.523%   $268.649   $268.65   $268.65   $268.60  
  Purchase #2 $172.78   10.540%   $190.991   $190.99   $191.00   $191.00  
  Purchase #3 $131.86   10.518%   $145.729   $145.73   $145.75   $145.70  
  Purchase #4 $248.89   12.185%   $279.2172   $279.22   $279.20   $279.20  
  Purchase #5 $242.54   11.431%   $270.2647   $270.26   $270.25   $270.30  
  Purchase #6 $233.90   13.334%   $265.0882   $265.09   $265.10   $265.10  
  Purchase #7 $114.95   10.624%   $127.1623   $127.16   $127.15   $127.20  
  7 purchase totals = $1,390.21       $1,547.1014   $1,547.10   $1,547.10   $1,547.10