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	$100.52	13.689%	$114.2802	$114.28	$114.30	$114.30
Purchase #2	$80.25	4.570%	$83.9174	$83.92	$83.90	$83.90
Purchase #3	$22.33	6.485%	$23.7781	$23.78	$23.80	$23.80
Purchase #4	$142.53	4.126%	$148.4108	$148.41	$148.40	$148.40
Purchase #5	$81.84	9.298%	$89.4495	$89.45	$89.45	$89.40
Purchase #6	$113.77	8.155%	$123.0479	$123.05	$123.05	$123.00
Purchase #7	$28.82	4.278%	$30.0529	$30.05	$30.05	$30.10
7 purchase totals =	$570.06		$612.9368	$612.94	$612.95	$612.90