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	$20.36	6.496%	$21.6826	$21.68	$21.70	$21.70
Purchase #2	$13.70	6.840%	$14.6371	$14.64	$14.65	$14.60
Purchase #3	$125.52	5.601%	$132.5504	$132.55	$132.55	$132.60
Purchase #4	$127.86	3.178%	$131.9234	$131.92	$131.90	$131.90
Purchase #5	$81.65	8.867%	$88.8899	$88.89	$88.90	$88.90
Purchase #6	$129.42	12.124%	$145.1109	$145.11	$145.10	$145.10
Purchase #7	$196.94	10.154%	$216.9373	$216.94	$216.95	$216.90
7 purchase totals =	$695.45		$751.7316	$751.73	$751.75	$751.70