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	$63.59	10.322%	$70.1538	$70.15	$70.15	$70.20
Purchase #2	$144.47	3.525%	$149.5626	$149.56	$149.55	$149.60
Purchase #3	$179.26	11.809%	$200.4288	$200.43	$200.45	$200.40
Purchase #4	$104.44	6.701%	$111.4385	$111.44	$111.45	$111.40
Purchase #5	$11.41	9.104%	$12.4488	$12.45	$12.45	$12.40
Purchase #6	$38.49	11.314%	$42.8448	$42.84	$42.85	$42.80
Purchase #7	$67.45	11.401%	$75.14	$75.14	$75.15	$75.10
7 purchase totals =	$609.11		$662.0173	$662.01	$662.05	$661.90