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	$226.34	8.370%	$245.2847	$245.28	$245.30	$245.30
Purchase #2	$35.51	13.554%	$40.323	$40.32	$40.30	$40.30
Purchase #3	$146.84	5.760%	$155.298	$155.30	$155.30	$155.30
Purchase #4	$40.60	5.488%	$42.8281	$42.83	$42.85	$42.80
Purchase #5	$55.91	13.822%	$63.6379	$63.64	$63.65	$63.60
Purchase #6	$104.28	12.714%	$117.5382	$117.54	$117.55	$117.50
Purchase #7	$169.29	3.461%	$175.1491	$175.15	$175.15	$175.10
7 purchase totals =	$778.77		$840.0590	$840.06	$840.10	$839.90