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	$176.26	9.440%	$192.8989	$192.90	$192.90	$192.90
Purchase #2	$75.77	12.389%	$85.1571	$85.16	$85.15	$85.20
Purchase #3	$136.75	5.510%	$144.2849	$144.28	$144.30	$144.30
Purchase #4	$110.69	8.870%	$120.5082	$120.51	$120.50	$120.50
Purchase #5	$38.51	8.133%	$41.642	$41.64	$41.65	$41.60
Purchase #6	$73.40	6.118%	$77.8906	$77.89	$77.90	$77.90
Purchase #7	$150.74	5.793%	$159.4724	$159.47	$159.45	$159.50
7 purchase totals =	$762.12		$821.8541	$821.85	$821.85	$821.90