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	$102.32	4.872%	$107.305	$107.31	$107.30	$107.30
Purchase #2	$35.82	12.491%	$40.2943	$40.29	$40.30	$40.30
Purchase #3	$49.93	11.455%	$55.6495	$55.65	$55.65	$55.60
Purchase #4	$94.57	4.686%	$99.0016	$99.00	$99.00	$99.00
Purchase #5	$13.93	9.872%	$15.3052	$15.31	$15.30	$15.30
Purchase #6	$152.43	8.111%	$164.7936	$164.79	$164.80	$164.80
Purchase #7	$189.80	4.766%	$198.8459	$198.85	$198.85	$198.80
7 purchase totals =	$638.80		$681.1951	$681.20	$681.20	$681.10