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	$37.27	8.315%	$40.369	$40.37	$40.35	$40.40
Purchase #2	$234.98	12.543%	$264.4535	$264.45	$264.45	$264.50
Purchase #3	$103.74	3.537%	$107.4093	$107.41	$107.40	$107.40
Purchase #4	$10.28	10.196%	$11.3281	$11.33	$11.35	$11.30
Purchase #5	$239.31	11.329%	$266.4214	$266.42	$266.40	$266.40
Purchase #6	$54.73	8.717%	$59.5008	$59.50	$59.50	$59.50
Purchase #7	$34.35	7.542%	$36.9407	$36.94	$36.95	$36.90
7 purchase totals =	$714.66		$786.4228	$786.42	$786.40	$786.40