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	$6.73	7.326%	$7.223	$7.22	$7.20	$7.20
Purchase #2	$61.37	13.119%	$69.4211	$69.42	$69.40	$69.40
Purchase #3	$133.28	3.251%	$137.6129	$137.61	$137.60	$137.60
Purchase #4	$98.40	8.655%	$106.9165	$106.92	$106.90	$106.90
Purchase #5	$157.74	4.320%	$164.5544	$164.55	$164.55	$164.60
Purchase #6	$134.61	4.852%	$141.1413	$141.14	$141.15	$141.10
Purchase #7	$42.89	6.372%	$45.623	$45.62	$45.60	$45.60
7 purchase totals =	$635.02		$672.4922	$672.48	$672.40	$672.40