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	$137.87	12.441%	$155.0224	$155.02	$155.00	$155.00
Purchase #2	$83.85	6.501%	$89.3011	$89.30	$89.30	$89.30
Purchase #3	$123.45	3.532%	$127.8103	$127.81	$127.80	$127.80
Purchase #4	$74.29	12.164%	$83.3266	$83.33	$83.35	$83.30
Purchase #5	$111.90	8.439%	$121.3432	$121.34	$121.35	$121.30
Purchase #6	$56.63	12.869%	$63.9177	$63.92	$63.90	$63.90
Purchase #7	$184.57	6.333%	$196.2588	$196.26	$196.25	$196.30
7 purchase totals =	$772.56		$836.9801	$836.98	$836.95	$836.90