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	$32.57	12.344%	$36.5904	$36.59	$36.60	$36.60
Purchase #2	$12.59	5.146%	$13.2379	$13.24	$13.25	$13.20
Purchase #3	$112.53	4.261%	$117.3249	$117.32	$117.30	$117.30
Purchase #4	$53.61	10.269%	$59.1152	$59.12	$59.10	$59.10
Purchase #5	$129.27	12.412%	$145.315	$145.32	$145.30	$145.30
Purchase #6	$175.75	11.461%	$195.8927	$195.89	$195.90	$195.90
Purchase #7	$239.90	11.184%	$266.7304	$266.73	$266.75	$266.70
7 purchase totals =	$756.22		$834.2065	$834.21	$834.20	$834.10