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	$205.98	10.116%	$226.8169	$226.82	$226.80	$226.80
Purchase #2	$213.87	12.224%	$240.0135	$240.01	$240.00	$240.00
Purchase #3	$61.26	5.788%	$64.8057	$64.81	$64.80	$64.80
Purchase #4	$173.46	9.714%	$190.3099	$190.31	$190.30	$190.30
Purchase #5	$247.49	7.382%	$265.7597	$265.76	$265.75	$265.80
Purchase #6	$55.89	6.761%	$59.6687	$59.67	$59.65	$59.70
Purchase #7	$148.87	9.361%	$162.8057	$162.81	$162.80	$162.80
7 purchase totals =	$1,106.82		$1,210.1801	$1,210.19	$1,210.10	$1,210.20