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	$30.32	9.142%	$33.0919	$33.09	$33.10	$33.10
Purchase #2	$123.88	4.851%	$129.8894	$129.89	$129.90	$129.90
Purchase #3	$175.29	8.599%	$190.3632	$190.36	$190.35	$190.40
Purchase #4	$149.83	11.400%	$166.9106	$166.91	$166.90	$166.90
Purchase #5	$88.74	3.655%	$91.9834	$91.98	$92.00	$92.00
Purchase #6	$221.83	10.103%	$244.2415	$244.24	$244.25	$244.20
Purchase #7	$76.63	8.464%	$83.116	$83.12	$83.10	$83.10
7 purchase totals =	$866.52		$939.5960	$939.59	$939.60	$939.60