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	$125.49	10.865%	$139.1245	$139.12	$139.10	$139.10
Purchase #2	$206.43	4.871%	$216.4852	$216.49	$216.50	$216.50
Purchase #3	$129.74	11.271%	$144.363	$144.36	$144.35	$144.40
Purchase #4	$202.37	4.403%	$211.2804	$211.28	$211.30	$211.30
Purchase #5	$99.31	12.752%	$111.974	$111.97	$111.95	$112.00
Purchase #6	$79.67	10.541%	$88.068	$88.07	$88.05	$88.10
Purchase #7	$159.47	10.258%	$175.8284	$175.83	$175.85	$175.80
7 purchase totals =	$1,002.48		$1,087.1235	$1,087.12	$1,087.10	$1,087.20