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	$123.81	12.647%	$139.4683	$139.47	$139.45	$139.50
Purchase #2	$60.32	11.648%	$67.3461	$67.35	$67.35	$67.30
Purchase #3	$210.60	3.252%	$217.4487	$217.45	$217.45	$217.40
Purchase #4	$239.70	3.785%	$248.7726	$248.77	$248.75	$248.80
Purchase #5	$92.51	8.251%	$100.143	$100.14	$100.15	$100.10
Purchase #6	$229.44	11.410%	$255.6191	$255.62	$255.60	$255.60
Purchase #7	$152.50	12.322%	$171.2911	$171.29	$171.30	$171.30
7 purchase totals =	$1,108.88		$1,200.0889	$1,200.09	$1,200.05	$1,200.00