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	$128.37	8.222%	$138.9246	$138.92	$138.90	$138.90
Purchase #2	$99.78	8.781%	$108.5417	$108.54	$108.55	$108.50
Purchase #3	$72.28	13.547%	$82.0718	$82.07	$82.05	$82.10
Purchase #4	$45.79	9.543%	$50.1597	$50.16	$50.15	$50.20
Purchase #5	$132.55	11.663%	$148.0093	$148.01	$148.00	$148.00
Purchase #6	$212.90	5.103%	$223.7643	$223.76	$223.75	$223.80
Purchase #7	$168.94	12.388%	$189.8683	$189.87	$189.85	$189.90
7 purchase totals =	$860.61		$941.3397	$941.33	$941.25	$941.40