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	$138.73	6.575%	$147.8515	$147.85	$147.85	$147.90
Purchase #2	$35.89	12.452%	$40.359	$40.36	$40.35	$40.40
Purchase #3	$209.55	6.780%	$223.7575	$223.76	$223.75	$223.80
Purchase #4	$49.36	10.449%	$54.5176	$54.52	$54.50	$54.50
Purchase #5	$147.99	7.435%	$158.9931	$158.99	$159.00	$159.00
Purchase #6	$131.28	6.513%	$139.8303	$139.83	$139.85	$139.80
Purchase #7	$244.70	10.683%	$270.8413	$270.84	$270.85	$270.80
7 purchase totals =	$957.50		$1,036.1503	$1,036.15	$1,036.15	$1,036.20