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	$55.49	6.605%	$59.1551	$59.16	$59.15	$59.20
Purchase #2	$69.74	4.418%	$72.8211	$72.82	$72.80	$72.80
Purchase #3	$53.94	7.732%	$58.1106	$58.11	$58.10	$58.10
Purchase #4	$113.35	12.835%	$127.8985	$127.90	$127.90	$127.90
Purchase #5	$33.73	9.233%	$36.8443	$36.84	$36.85	$36.80
Purchase #6	$25.95	5.451%	$27.3645	$27.36	$27.35	$27.40
Purchase #7	$19.75	9.350%	$21.5966	$21.60	$21.60	$21.60
7 purchase totals =	$371.95		$403.7907	$403.79	$403.75	$403.80