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	$56.73	6.697%	$60.5292	$60.53	$60.55	$60.50
Purchase #2	$138.73	12.853%	$156.561	$156.56	$156.55	$156.60
Purchase #3	$16.44	9.625%	$18.0224	$18.02	$18.00	$18.00
Purchase #4	$132.72	6.337%	$141.1305	$141.13	$141.15	$141.10
Purchase #5	$179.44	5.389%	$189.11	$189.11	$189.10	$189.10
Purchase #6	$72.55	8.302%	$78.5731	$78.57	$78.55	$78.60
Purchase #7	$167.86	5.244%	$176.6626	$176.66	$176.65	$176.70
7 purchase totals =	$764.47		$820.5888	$820.58	$820.55	$820.60