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	$150.56	6.425%	$160.2335	$160.23	$160.25	$160.20
Purchase #2	$67.45	6.641%	$71.9294	$71.93	$71.95	$71.90
Purchase #3	$13.44	5.541%	$14.1847	$14.18	$14.20	$14.20
Purchase #4	$142.76	6.537%	$152.0922	$152.09	$152.10	$152.10
Purchase #5	$115.78	13.192%	$131.0537	$131.05	$131.05	$131.10
Purchase #6	$78.95	5.593%	$83.3657	$83.37	$83.35	$83.40
Purchase #7	$82.31	9.856%	$90.4225	$90.42	$90.40	$90.40
7 purchase totals =	$651.25		$703.2817	$703.27	$703.30	$703.30