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	$38.73	10.834%	$42.926	$42.93	$42.95	$42.90
Purchase #2	$75.84	9.739%	$83.2261	$83.23	$83.25	$83.20
Purchase #3	$143.74	12.133%	$161.18	$161.18	$161.20	$161.20
Purchase #4	$95.70	6.518%	$101.9377	$101.94	$101.95	$101.90
Purchase #5	$30.32	6.369%	$32.2511	$32.25	$32.25	$32.30
Purchase #6	$72.74	8.205%	$78.7083	$78.71	$78.70	$78.70
Purchase #7	$132.54	8.121%	$143.3036	$143.30	$143.30	$143.30
7 purchase totals =	$589.61		$643.5328	$643.54	$643.60	$643.50