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	$28.69	8.821%	$31.2207	$31.22	$31.20	$31.20
Purchase #2	$235.43	12.535%	$264.9412	$264.94	$264.95	$264.90
Purchase #3	$210.76	13.512%	$239.2379	$239.24	$239.25	$239.20
Purchase #4	$106.95	4.506%	$111.7692	$111.77	$111.75	$111.80
Purchase #5	$161.66	11.411%	$180.107	$180.11	$180.10	$180.10
Purchase #6	$247.43	7.692%	$266.4623	$266.46	$266.45	$266.50
Purchase #7	$53.66	11.472%	$59.8159	$59.82	$59.80	$59.80
7 purchase totals =	$1,044.58		$1,153.5542	$1,153.56	$1,153.50	$1,153.50