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	$129.89	13.722%	$147.7135	$147.71	$147.70	$147.70
Purchase #2	$117.43	6.429%	$124.9796	$124.98	$125.00	$125.00
Purchase #3	$48.60	10.247%	$53.58	$53.58	$53.60	$53.60
Purchase #4	$31.47	5.700%	$33.2638	$33.26	$33.25	$33.30
Purchase #5	$144.85	11.681%	$161.7699	$161.77	$161.75	$161.80
Purchase #6	$118.83	10.433%	$131.2275	$131.23	$131.25	$131.20
Purchase #7	$161.44	10.275%	$178.028	$178.03	$178.05	$178.00
7 purchase totals =	$752.51		$830.5623	$830.56	$830.60	$830.60