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	$35.39	13.684%	$40.2328	$40.23	$40.25	$40.20
Purchase #2	$118.45	7.181%	$126.9559	$126.96	$126.95	$127.00
Purchase #3	$78.31	5.303%	$82.4628	$82.46	$82.45	$82.50
Purchase #4	$77.35	11.183%	$86.0001	$86.00	$86.00	$86.00
Purchase #5	$129.67	10.710%	$143.5577	$143.56	$143.55	$143.60
Purchase #6	$30.40	5.487%	$32.068	$32.07	$32.05	$32.10
Purchase #7	$127.36	7.109%	$136.414	$136.41	$136.40	$136.40
7 purchase totals =	$596.93		$647.6913	$647.69	$647.65	$647.80