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	$214.47	12.261%	$240.7662	$240.77	$240.75	$240.80
Purchase #2	$169.51	7.455%	$182.147	$182.15	$182.15	$182.10
Purchase #3	$45.43	11.844%	$50.8107	$50.81	$50.80	$50.80
Purchase #4	$154.40	8.712%	$167.8513	$167.85	$167.85	$167.90
Purchase #5	$69.35	4.510%	$72.4777	$72.48	$72.50	$72.50
Purchase #6	$216.33	13.342%	$245.1927	$245.19	$245.20	$245.20
Purchase #7	$17.27	9.708%	$18.9466	$18.95	$18.95	$18.90
7 purchase totals =	$886.76		$978.1922	$978.20	$978.20	$978.20