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	$33.42	12.295%	$37.529	$37.53	$37.55	$37.50
Purchase #2	$64.61	11.693%	$72.1648	$72.16	$72.15	$72.20
Purchase #3	$202.86	13.140%	$229.5158	$229.52	$229.50	$229.50
Purchase #4	$113.64	4.441%	$118.6868	$118.69	$118.70	$118.70
Purchase #5	$110.46	8.640%	$120.0037	$120.00	$120.00	$120.00
Purchase #6	$173.50	10.179%	$191.1606	$191.16	$191.15	$191.20
Purchase #7	$168.54	13.751%	$191.7159	$191.72	$191.70	$191.70
7 purchase totals =	$867.03		$960.7766	$960.78	$960.75	$960.80