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	$145.74	6.466%	$155.1635	$155.16	$155.15	$155.20
Purchase #2	$11.38	3.518%	$11.7803	$11.78	$11.80	$11.80
Purchase #3	$221.42	7.538%	$238.1106	$238.11	$238.10	$238.10
Purchase #4	$127.86	7.744%	$137.7615	$137.76	$137.75	$137.80
Purchase #5	$158.45	11.300%	$176.3549	$176.35	$176.35	$176.40
Purchase #6	$142.32	6.244%	$151.2065	$151.21	$151.20	$151.20
Purchase #7	$45.35	6.740%	$48.4066	$48.41	$48.40	$48.40
7 purchase totals =	$852.52		$918.7839	$918.78	$918.75	$918.90