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 $192.82   6.491%   $205.3359   $205.34   $205.35   $205.30  
  Purchase #2 $240.96   9.873%   $264.75   $264.75   $264.75   $264.80  
  Purchase #3 $153.41   11.261%   $170.6855   $170.69   $170.70   $170.70  
  Purchase #4 $119.97   11.143%   $133.3383   $133.34   $133.35   $133.30  
  Purchase #5 $15.58   13.470%   $17.6786   $17.68   $17.70   $17.70  
  Purchase #6 $127.53   3.745%   $132.306   $132.31   $132.30   $132.30  
  Purchase #7 $102.85   8.861%   $111.9635   $111.96   $111.95   $112.00  
  7 purchase totals = $953.12       $1,036.0578   $1,036.07   $1,036.10   $1,036.10