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	$102.51	13.430%	$116.2771	$116.28	$116.30	$116.30
Purchase #2	$54.87	8.304%	$59.4264	$59.43	$59.45	$59.40
Purchase #3	$136.89	3.543%	$141.74	$141.74	$141.75	$141.70
Purchase #4	$69.52	13.385%	$78.8253	$78.83	$78.85	$78.80
Purchase #5	$79.81	7.103%	$85.4789	$85.48	$85.50	$85.50
Purchase #6	$25.97	6.387%	$27.6287	$27.63	$27.65	$27.60
Purchase #7	$122.37	7.180%	$131.1562	$131.16	$131.15	$131.20
7 purchase totals =	$591.94		$640.5326	$640.55	$640.65	$640.50