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 $107.82   9.743%   $118.3249   $118.32   $118.30   $118.30  
  Purchase #2 $216.41   3.669%   $224.3501   $224.35   $224.35   $224.40  
  Purchase #3 $241.93   5.131%   $254.3434   $254.34   $254.35   $254.30  
  Purchase #4 $38.77   5.762%   $41.0039   $41.00   $41.00   $41.00  
  Purchase #5 $245.58   8.206%   $265.7323   $265.73   $265.75   $265.70  
  Purchase #6 $65.99   7.699%   $71.0706   $71.07   $71.05   $71.10  
  Purchase #7 $58.33   10.201%   $64.2802   $64.28   $64.30   $64.30  
  7 purchase totals = $974.83       $1,039.1054   $1,039.09   $1,039.10   $1,039.10