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	$15.81	9.724%	$17.3474	$17.35	$17.35	$17.30
Purchase #2	$152.83	8.232%	$165.411	$165.41	$165.40	$165.40
Purchase #3	$69.93	6.755%	$74.6538	$74.65	$74.65	$74.70
Purchase #4	$209.73	9.329%	$229.2957	$229.30	$229.30	$229.30
Purchase #5	$72.43	7.783%	$78.0672	$78.07	$78.05	$78.10
Purchase #6	$179.47	9.507%	$196.5322	$196.53	$196.55	$196.50
Purchase #7	$150.78	13.663%	$171.3811	$171.38	$171.40	$171.40
7 purchase totals =	$850.98		$932.6884	$932.69	$932.70	$932.70