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	$230.38	7.102%	$246.7416	$246.74	$246.75	$246.70
Purchase #2	$80.27	11.123%	$89.1984	$89.20	$89.20	$89.20
Purchase #3	$207.65	10.222%	$228.876	$228.88	$228.90	$228.90
Purchase #4	$64.63	9.319%	$70.6529	$70.65	$70.65	$70.70
Purchase #5	$88.70	9.247%	$96.9021	$96.90	$96.90	$96.90
Purchase #6	$53.27	12.734%	$60.0534	$60.05	$60.05	$60.10
Purchase #7	$118.59	4.117%	$123.4724	$123.47	$123.45	$123.50
7 purchase totals =	$843.49		$915.8968	$915.89	$915.90	$916.00