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	$143.48	6.852%	$153.3112	$153.31	$153.30	$153.30
Purchase #2	$153.77	11.296%	$171.1399	$171.14	$171.15	$171.10
Purchase #3	$55.90	11.194%	$62.1574	$62.16	$62.15	$62.20
Purchase #4	$85.63	4.511%	$89.4928	$89.49	$89.50	$89.50
Purchase #5	$244.32	7.592%	$262.8688	$262.87	$262.85	$262.90
Purchase #6	$5.94	5.495%	$6.2664	$6.27	$6.25	$6.30
Purchase #7	$118.49	9.329%	$129.5439	$129.54	$129.55	$129.50
7 purchase totals =	$807.53		$874.7804	$874.78	$874.75	$874.80