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	$183.56	3.584%	$190.1388	$190.14	$190.15	$190.10
Purchase #2	$34.88	12.480%	$39.233	$39.23	$39.25	$39.20
Purchase #3	$90.52	13.427%	$102.6741	$102.67	$102.65	$102.70
Purchase #4	$133.42	12.707%	$150.3737	$150.37	$150.35	$150.40
Purchase #5	$69.90	10.258%	$77.0703	$77.07	$77.05	$77.10
Purchase #6	$168.94	9.666%	$185.2697	$185.27	$185.25	$185.30
Purchase #7	$148.96	5.302%	$156.8579	$156.86	$156.85	$156.90
7 purchase totals =	$830.18		$901.6175	$901.61	$901.55	$901.70