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 $165.50   11.561%   $184.6335   $184.63   $184.65   $184.60  
  Purchase #2 $172.79   13.417%   $195.9732   $195.97   $195.95   $196.00  
  Purchase #3 $92.33   13.471%   $104.7678   $104.77   $104.75   $104.80  
  Purchase #4 $248.99   6.725%   $265.7346   $265.73   $265.75   $265.70  
  Purchase #5 $5.33   8.465%   $5.7812   $5.78   $5.80   $5.80  
  Purchase #6 $63.78   12.468%   $71.7321   $71.73   $71.75   $71.70  
  Purchase #7 $78.91   4.554%   $82.5036   $82.50   $82.50   $82.50  
  7 purchase totals = $827.63       $911.1260   $911.11   $911.15   $911.10