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	$19.65	9.456%	$21.5081	$21.51	$21.50	$21.50
Purchase #2	$171.60	10.707%	$189.9732	$189.97	$189.95	$190.00
Purchase #3	$109.78	12.417%	$123.4114	$123.41	$123.40	$123.40
Purchase #4	$92.94	9.318%	$101.6001	$101.60	$101.60	$101.60
Purchase #5	$92.67	12.255%	$104.0267	$104.03	$104.05	$104.00
Purchase #6	$225.90	6.548%	$240.6919	$240.69	$240.70	$240.70
Purchase #7	$36.51	3.177%	$37.6699	$37.67	$37.65	$37.70
7 purchase totals =	$749.05		$818.8813	$818.88	$818.85	$818.90