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	$81.78	12.145%	$91.7122	$91.71	$91.70	$91.70
Purchase #2	$33.54	4.353%	$35	$35.00	$35.00	$35.00
Purchase #3	$87.85	12.771%	$99.0693	$99.07	$99.05	$99.10
Purchase #4	$29.81	8.859%	$32.4509	$32.45	$32.45	$32.50
Purchase #5	$61.69	4.484%	$64.4562	$64.46	$64.45	$64.50
Purchase #6	$102.82	6.164%	$109.1578	$109.16	$109.15	$109.20
Purchase #7	$154.65	3.538%	$160.1215	$160.12	$160.10	$160.10
7 purchase totals =	$552.14		$591.9679	$591.97	$591.90	$592.10