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	$96.74	6.354%	$102.8869	$102.89	$102.90	$102.90
Purchase #2	$25.45	7.785%	$27.4313	$27.43	$27.45	$27.40
Purchase #3	$98.91	12.383%	$111.158	$111.16	$111.15	$111.20
Purchase #4	$36.56	12.572%	$41.1563	$41.16	$41.15	$41.20
Purchase #5	$48.89	3.452%	$50.5777	$50.58	$50.60	$50.60
Purchase #6	$13.51	7.362%	$14.5046	$14.50	$14.50	$14.50
Purchase #7	$42.69	4.862%	$44.7656	$44.77	$44.75	$44.80
7 purchase totals =	$362.75		$392.4804	$392.49	$392.50	$392.60