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 $83.51   12.779%   $94.1817   $94.18   $94.20   $94.20  
  Purchase #2 $95.55   9.263%   $104.4008   $104.40   $104.40   $104.40  
  Purchase #3 $114.68   4.171%   $119.4633   $119.46   $119.45   $119.50  
  Purchase #4 $169.72   9.306%   $185.5141   $185.51   $185.50   $185.50  
  Purchase #5 $44.69   12.563%   $50.3044   $50.30   $50.30   $50.30  
  Purchase #6 $242.30   4.151%   $252.3579   $252.36   $252.35   $252.40  
  Purchase #7 $50.32   11.279%   $55.9956   $56.00   $56.00   $56.00  
  7 purchase totals = $800.77       $862.2178   $862.21   $862.20   $862.30