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	$159.77	3.805%	$165.8492	$165.85	$165.85	$165.80
Purchase #2	$40.48	3.505%	$41.8988	$41.90	$41.90	$41.90
Purchase #3	$160.52	9.396%	$175.6025	$175.60	$175.60	$175.60
Purchase #4	$209.59	8.586%	$227.5854	$227.59	$227.60	$227.60
Purchase #5	$85.45	6.222%	$90.7667	$90.77	$90.75	$90.80
Purchase #6	$140.27	6.157%	$148.9064	$148.91	$148.90	$148.90
Purchase #7	$84.73	3.643%	$87.8167	$87.82	$87.80	$87.80
7 purchase totals =	$880.81		$938.4257	$938.44	$938.40	$938.40