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	$50.84	12.335%	$57.1111	$57.11	$57.10	$57.10
Purchase #2	$229.78	10.327%	$253.5094	$253.51	$253.50	$253.50
Purchase #3	$60.73	7.625%	$65.3607	$65.36	$65.35	$65.40
Purchase #4	$50.68	7.480%	$54.4709	$54.47	$54.45	$54.50
Purchase #5	$38.45	6.177%	$40.8251	$40.83	$40.85	$40.80
Purchase #6	$239.36	12.695%	$269.7468	$269.75	$269.75	$269.70
Purchase #7	$250.43	8.472%	$271.6464	$271.65	$271.65	$271.60
7 purchase totals =	$920.27		$1,012.6704	$1,012.68	$1,012.65	$1,012.60