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	$50.25	7.643%	$54.0906	$54.09	$54.10	$54.10
Purchase #2	$89.90	10.309%	$99.1678	$99.17	$99.15	$99.20
Purchase #3	$129.48	8.815%	$140.8937	$140.89	$140.90	$140.90
Purchase #4	$53.36	3.240%	$55.0889	$55.09	$55.10	$55.10
Purchase #5	$83.63	11.296%	$93.0768	$93.08	$93.10	$93.10
Purchase #6	$100.49	3.667%	$104.175	$104.18	$104.20	$104.20
Purchase #7	$32.55	13.687%	$37.0051	$37.01	$37.00	$37.00
7 purchase totals =	$539.66		$583.4979	$583.51	$583.55	$583.60