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	$84.85	5.278%	$89.3284	$89.33	$89.35	$89.30
Purchase #2	$173.87	13.251%	$196.9095	$196.91	$196.90	$196.90
Purchase #3	$220.32	3.680%	$228.4278	$228.43	$228.45	$228.40
Purchase #4	$56.96	3.278%	$58.8271	$58.83	$58.85	$58.80
Purchase #5	$207.35	12.221%	$232.6902	$232.69	$232.70	$232.70
Purchase #6	$118.80	9.683%	$130.3034	$130.30	$130.30	$130.30
Purchase #7	$30.88	9.788%	$33.9025	$33.90	$33.90	$33.90
7 purchase totals =	$893.03		$970.3889	$970.39	$970.45	$970.30