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	$109.35	12.256%	$122.7519	$122.75	$122.75	$122.80
Purchase #2	$39.77	13.745%	$45.2364	$45.24	$45.25	$45.20
Purchase #3	$33.36	7.287%	$35.7909	$35.79	$35.80	$35.80
Purchase #4	$37.30	5.740%	$39.441	$39.44	$39.45	$39.40
Purchase #5	$138.39	3.625%	$143.4066	$143.41	$143.40	$143.40
Purchase #6	$37.44	8.290%	$40.5438	$40.54	$40.55	$40.50
Purchase #7	$91.38	13.217%	$103.4577	$103.46	$103.45	$103.50
7 purchase totals =	$486.99		$530.6283	$530.63	$530.65	$530.60