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	$77.29	3.190%	$79.7556	$79.76	$79.75	$79.80
Purchase #2	$173.53	10.105%	$191.0652	$191.07	$191.05	$191.10
Purchase #3	$249.25	5.644%	$263.3177	$263.32	$263.30	$263.30
Purchase #4	$153.89	7.743%	$165.8057	$165.81	$165.80	$165.80
Purchase #5	$123.70	3.196%	$127.6535	$127.65	$127.65	$127.70
Purchase #6	$118.33	8.405%	$128.2756	$128.28	$128.30	$128.30
Purchase #7	$168.78	6.238%	$179.3085	$179.31	$179.30	$179.30
7 purchase totals =	$1,064.77		$1,135.1818	$1,135.20	$1,135.15	$1,135.30