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	$91.54	11.476%	$102.0451	$102.05	$102.05	$102.00
Purchase #2	$185.75	3.312%	$191.902	$191.90	$191.90	$191.90
Purchase #3	$43.58	4.200%	$45.4104	$45.41	$45.40	$45.40
Purchase #4	$28.42	7.152%	$30.4526	$30.45	$30.45	$30.50
Purchase #5	$146.45	8.381%	$158.724	$158.72	$158.70	$158.70
Purchase #6	$116.92	7.681%	$125.9006	$125.90	$125.90	$125.90
Purchase #7	$99.55	3.853%	$103.3857	$103.39	$103.40	$103.40
7 purchase totals =	$712.21		$757.8204	$757.82	$757.80	$757.80