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	$85.47	9.495%	$93.5854	$93.59	$93.60	$93.60
Purchase #2	$205.58	9.743%	$225.6097	$225.61	$225.60	$225.60
Purchase #3	$57.54	3.113%	$59.3312	$59.33	$59.35	$59.30
Purchase #4	$97.30	8.534%	$105.6036	$105.60	$105.60	$105.60
Purchase #5	$6.85	7.654%	$7.3743	$7.37	$7.35	$7.40
Purchase #6	$111.65	10.601%	$123.486	$123.49	$123.50	$123.50
Purchase #7	$62.99	8.735%	$68.4922	$68.49	$68.50	$68.50
7 purchase totals =	$627.38		$683.4824	$683.48	$683.50	$683.50