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	$72.59	13.411%	$82.325	$82.33	$82.35	$82.30
Purchase #2	$176.61	11.130%	$196.2667	$196.27	$196.25	$196.30
Purchase #3	$107.58	4.322%	$112.2296	$112.23	$112.25	$112.20
Purchase #4	$131.36	13.554%	$149.1645	$149.16	$149.15	$149.20
Purchase #5	$87.56	13.774%	$99.6205	$99.62	$99.60	$99.60
Purchase #6	$122.55	4.196%	$127.6922	$127.69	$127.70	$127.70
Purchase #7	$212.40	5.245%	$223.5404	$223.54	$223.55	$223.50
7 purchase totals =	$910.65		$990.8389	$990.84	$990.85	$990.80