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 $114.59   9.627%   $125.6216   $125.62   $125.60   $125.60  
  Purchase #2 $120.37   12.464%   $135.3729   $135.37   $135.35   $135.40  
  Purchase #3 $41.38   12.188%   $46.4234   $46.42   $46.40   $46.40  
  Purchase #4 $194.64   6.294%   $206.8906   $206.89   $206.90   $206.90  
  Purchase #5 $165.44   13.701%   $188.1069   $188.11   $188.10   $188.10  
  Purchase #6 $78.71   7.299%   $84.455   $84.46   $84.45   $84.50  
  Purchase #7 $204.99   4.303%   $213.8107   $213.81   $213.80   $213.80  
  7 purchase totals = $920.12       $1,000.6811   $1,000.68   $1,000.60   $1,000.70