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	$45.90	9.828%	$50.4111	$50.41	$50.40	$50.40
Purchase #2	$142.69	8.718%	$155.1297	$155.13	$155.15	$155.10
Purchase #3	$77.32	12.305%	$86.8342	$86.83	$86.85	$86.80
Purchase #4	$153.60	13.672%	$174.6002	$174.60	$174.60	$174.60
Purchase #5	$87.55	8.809%	$95.2623	$95.26	$95.25	$95.30
Purchase #6	$133.53	9.611%	$146.3636	$146.36	$146.35	$146.40
Purchase #7	$187.94	4.318%	$196.0552	$196.06	$196.05	$196.10
7 purchase totals =	$828.53		$904.6563	$904.65	$904.65	$904.70