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	$20.75	4.414%	$21.6659	$21.67	$21.65	$21.70
Purchase #2	$26.31	5.802%	$27.8365	$27.84	$27.85	$27.80
Purchase #3	$31.44	9.797%	$34.5202	$34.52	$34.50	$34.50
Purchase #4	$47.59	6.179%	$50.5306	$50.53	$50.55	$50.50
Purchase #5	$92.26	7.774%	$99.4323	$99.43	$99.45	$99.40
Purchase #6	$87.95	13.184%	$99.5453	$99.55	$99.55	$99.50
Purchase #7	$34.27	6.550%	$36.5147	$36.51	$36.50	$36.50
7 purchase totals =	$340.57		$370.0455	$370.05	$370.05	$369.90