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	$137.30	6.615%	$146.3824	$146.38	$146.40	$146.40
Purchase #2	$117.32	12.860%	$132.4074	$132.41	$132.40	$132.40
Purchase #3	$169.50	12.842%	$191.2672	$191.27	$191.25	$191.30
Purchase #4	$135.74	10.792%	$150.3891	$150.39	$150.40	$150.40
Purchase #5	$26.32	8.473%	$28.5501	$28.55	$28.55	$28.60
Purchase #6	$48.41	3.571%	$50.1387	$50.14	$50.15	$50.10
Purchase #7	$205.64	5.224%	$216.3826	$216.38	$216.40	$216.40
7 purchase totals =	$840.23		$915.5175	$915.52	$915.55	$915.60