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	$42.28	9.825%	$46.434	$46.43	$46.45	$46.40
Purchase #2	$137.70	6.795%	$147.0567	$147.06	$147.05	$147.10
Purchase #3	$18.40	10.436%	$20.3202	$20.32	$20.30	$20.30
Purchase #4	$38.50	9.371%	$42.1078	$42.11	$42.10	$42.10
Purchase #5	$139.78	12.721%	$157.5614	$157.56	$157.55	$157.60
Purchase #6	$168.75	12.698%	$190.1779	$190.18	$190.20	$190.20
Purchase #7	$55.58	13.454%	$63.0577	$63.06	$63.05	$63.10
7 purchase totals =	$600.99		$666.7157	$666.72	$666.70	$666.80