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	$71.55	11.233%	$79.5872	$79.59	$79.60	$79.60
Purchase #2	$164.52	13.633%	$186.949	$186.95	$186.95	$186.90
Purchase #3	$234.51	12.379%	$263.54	$263.54	$263.55	$263.50
Purchase #4	$100.69	11.196%	$111.9633	$111.96	$111.95	$112.00
Purchase #5	$137.35	9.552%	$150.4697	$150.47	$150.45	$150.50
Purchase #6	$37.92	4.829%	$39.7512	$39.75	$39.75	$39.80
Purchase #7	$90.79	9.569%	$99.4777	$99.48	$99.50	$99.50
7 purchase totals =	$837.33		$931.7381	$931.74	$931.75	$931.80