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	$83.87	7.797%	$90.4093	$90.41	$90.40	$90.40
Purchase #2	$87.61	13.247%	$99.2157	$99.22	$99.20	$99.20
Purchase #3	$44.70	6.122%	$47.4365	$47.44	$47.45	$47.40
Purchase #4	$130.42	8.572%	$141.5996	$141.60	$141.60	$141.60
Purchase #5	$29.53	13.612%	$33.5496	$33.55	$33.55	$33.50
Purchase #6	$173.74	10.465%	$191.9219	$191.92	$191.90	$191.90
Purchase #7	$124.45	6.651%	$132.7272	$132.73	$132.75	$132.70
7 purchase totals =	$674.32		$736.8598	$736.87	$736.85	$736.70