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	$188.32	6.629%	$200.8037	$200.80	$200.80	$200.80
Purchase #2	$64.91	5.505%	$68.4833	$68.48	$68.50	$68.50
Purchase #3	$228.73	11.853%	$255.8414	$255.84	$255.85	$255.80
Purchase #4	$78.75	8.469%	$85.4193	$85.42	$85.40	$85.40
Purchase #5	$90.97	11.316%	$101.2642	$101.26	$101.25	$101.30
Purchase #6	$101.69	7.793%	$109.6147	$109.61	$109.60	$109.60
Purchase #7	$153.53	10.174%	$169.1501	$169.15	$169.15	$169.20
7 purchase totals =	$906.90		$990.5767	$990.56	$990.55	$990.60