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 $184.99   10.136%   $203.7406   $203.74   $203.75   $203.70  
  Purchase #2 $44.56   6.492%   $47.4528   $47.45   $47.45   $47.50  
  Purchase #3 $132.82   8.874%   $144.6064   $144.61   $144.60   $144.60  
  Purchase #4 $199.28   10.847%   $220.8959   $220.90   $220.90   $220.90  
  Purchase #5 $192.91   13.149%   $218.2757   $218.28   $218.30   $218.30  
  Purchase #6 $104.93   4.194%   $109.3308   $109.33   $109.35   $109.30  
  Purchase #7 $165.47   10.206%   $182.3579   $182.36   $182.35   $182.40  
  7 purchase totals = $1,024.96       $1,126.6601   $1,126.67   $1,126.70   $1,126.70