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	$77.81	11.651%	$86.8756	$86.88	$86.90	$86.90
Purchase #2	$91.73	11.707%	$102.4688	$102.47	$102.45	$102.50
Purchase #3	$127.95	13.580%	$145.3256	$145.33	$145.35	$145.30
Purchase #4	$34.37	13.865%	$39.1354	$39.14	$39.15	$39.10
Purchase #5	$171.42	8.396%	$185.8124	$185.81	$185.80	$185.80
Purchase #6	$32.98	4.452%	$34.4483	$34.45	$34.45	$34.40
Purchase #7	$144.63	8.751%	$157.2866	$157.29	$157.30	$157.30
7 purchase totals =	$680.89		$751.3527	$751.37	$751.40	$751.30