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	$139.70	13.726%	$158.8752	$158.88	$158.90	$158.90
Purchase #2	$62.83	7.817%	$67.7414	$67.74	$67.75	$67.70
Purchase #3	$173.78	8.479%	$188.5148	$188.51	$188.50	$188.50
Purchase #4	$237.47	10.438%	$262.2571	$262.26	$262.25	$262.30
Purchase #5	$126.46	9.224%	$138.1247	$138.12	$138.10	$138.10
Purchase #6	$85.48	6.184%	$90.7661	$90.77	$90.75	$90.80
Purchase #7	$153.87	11.362%	$171.3527	$171.35	$171.35	$171.40
7 purchase totals =	$979.59		$1,077.6320	$1,077.63	$1,077.60	$1,077.70