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	$92.81	6.790%	$99.1118	$99.11	$99.10	$99.10
Purchase #2	$83.86	7.337%	$90.0128	$90.01	$90.00	$90.00
Purchase #3	$127.78	3.125%	$131.7731	$131.77	$131.75	$131.80
Purchase #4	$165.89	4.609%	$173.5359	$173.54	$173.55	$173.50
Purchase #5	$93.63	11.856%	$104.7308	$104.73	$104.75	$104.70
Purchase #6	$61.41	4.578%	$64.2213	$64.22	$64.20	$64.20
Purchase #7	$59.51	13.820%	$67.7343	$67.73	$67.75	$67.70
7 purchase totals =	$684.89		$731.1200	$731.11	$731.10	$731.00