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	$166.34	11.794%	$185.9581	$185.96	$185.95	$186.00
Purchase #2	$32.82	9.486%	$35.9333	$35.93	$35.95	$35.90
Purchase #3	$97.57	8.478%	$105.842	$105.84	$105.85	$105.80
Purchase #4	$43.90	10.337%	$48.4379	$48.44	$48.45	$48.40
Purchase #5	$135.92	11.141%	$151.0628	$151.06	$151.05	$151.10
Purchase #6	$91.44	9.826%	$100.4249	$100.42	$100.40	$100.40
Purchase #7	$39.74	11.107%	$44.1539	$44.15	$44.15	$44.20
7 purchase totals =	$607.73		$671.8129	$671.80	$671.80	$671.80