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	$91.78	5.150%	$96.5067	$96.51	$96.50	$96.50
Purchase #2	$102.79	8.801%	$111.8365	$111.84	$111.85	$111.80
Purchase #3	$129.25	9.533%	$141.5714	$141.57	$141.55	$141.60
Purchase #4	$157.70	7.586%	$169.6631	$169.66	$169.65	$169.70
Purchase #5	$129.36	11.461%	$144.1859	$144.19	$144.20	$144.20
Purchase #6	$50.59	3.749%	$52.4866	$52.49	$52.50	$52.50
Purchase #7	$30.59	4.244%	$31.8882	$31.89	$31.90	$31.90
7 purchase totals =	$692.06		$748.1384	$748.15	$748.15	$748.20