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	$101.57	8.853%	$110.562	$110.56	$110.55	$110.60
Purchase #2	$192.90	9.610%	$211.4377	$211.44	$211.45	$211.40
Purchase #3	$93.60	7.563%	$100.679	$100.68	$100.70	$100.70
Purchase #4	$105.96	10.294%	$116.8675	$116.87	$116.85	$116.90
Purchase #5	$190.30	12.451%	$213.9943	$213.99	$214.00	$214.00
Purchase #6	$85.39	4.251%	$89.0199	$89.02	$89.00	$89.00
Purchase #7	$59.45	13.214%	$67.3057	$67.31	$67.30	$67.30
7 purchase totals =	$829.17		$909.8661	$909.87	$909.85	$909.90