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	$131.97	4.378%	$137.7476	$137.75	$137.75	$137.70
Purchase #2	$56.81	9.390%	$62.1445	$62.14	$62.15	$62.10
Purchase #3	$61.90	13.361%	$70.1705	$70.17	$70.15	$70.20
Purchase #4	$88.66	3.630%	$91.8784	$91.88	$91.90	$91.90
Purchase #5	$88.50	3.252%	$91.378	$91.38	$91.40	$91.40
Purchase #6	$14.45	5.353%	$15.2235	$15.22	$15.20	$15.20
Purchase #7	$85.37	4.257%	$89.0042	$89.00	$89.00	$89.00
7 purchase totals =	$527.66		$557.5467	$557.54	$557.55	$557.50