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	$229.56	11.252%	$255.3901	$255.39	$255.40	$255.40
Purchase #2	$88.60	13.746%	$100.779	$100.78	$100.80	$100.80
Purchase #3	$158.43	5.262%	$166.7666	$166.77	$166.75	$166.80
Purchase #4	$180.30	7.717%	$194.2138	$194.21	$194.20	$194.20
Purchase #5	$168.71	4.738%	$176.7035	$176.70	$176.70	$176.70
Purchase #6	$195.91	11.597%	$218.6297	$218.63	$218.65	$218.60
Purchase #7	$89.62	6.840%	$95.75	$95.75	$95.75	$95.80
7 purchase totals =	$1,111.13		$1,208.2327	$1,208.23	$1,208.25	$1,208.30