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 $34.91   6.463%   $37.1662   $37.17   $37.15   $37.20  
  Purchase #2 $224.81   8.707%   $244.3842   $244.38   $244.40   $244.40  
  Purchase #3 $233.94   4.375%   $244.1749   $244.17   $244.15   $244.20  
  Purchase #4 $152.55   7.207%   $163.5443   $163.54   $163.55   $163.50  
  Purchase #5 $94.94   13.271%   $107.5395   $107.54   $107.55   $107.50  
  Purchase #6 $96.97   7.747%   $104.4823   $104.48   $104.50   $104.50  
  Purchase #7 $125.36   7.572%   $134.8523   $134.85   $134.85   $134.90  
  7 purchase totals = $963.48       $1,036.1437   $1,036.13   $1,036.15   $1,036.20