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	$53.51	8.260%	$57.9299	$57.93	$57.95	$57.90
Purchase #2	$226.61	5.734%	$239.6038	$239.60	$239.60	$239.60
Purchase #3	$245.51	10.531%	$271.3647	$271.36	$271.35	$271.40
Purchase #4	$36.60	11.562%	$40.8317	$40.83	$40.85	$40.80
Purchase #5	$204.96	4.162%	$213.4904	$213.49	$213.50	$213.50
Purchase #6	$79.32	7.672%	$85.4054	$85.41	$85.40	$85.40
Purchase #7	$142.52	10.714%	$157.7896	$157.79	$157.80	$157.80
7 purchase totals =	$989.03		$1,066.4155	$1,066.41	$1,066.45	$1,066.40