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	$59.42	8.682%	$64.5788	$64.58	$64.60	$64.60
Purchase #2	$142.83	8.604%	$155.1191	$155.12	$155.10	$155.10
Purchase #3	$242.32	5.805%	$256.3867	$256.39	$256.40	$256.40
Purchase #4	$117.97	7.753%	$127.1162	$127.12	$127.10	$127.10
Purchase #5	$165.77	3.507%	$171.5836	$171.58	$171.60	$171.60
Purchase #6	$53.43	3.659%	$55.385	$55.39	$55.40	$55.40
Purchase #7	$137.79	11.732%	$153.9555	$153.96	$153.95	$154.00
7 purchase totals =	$919.53		$984.1249	$984.14	$984.15	$984.20