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	$16.57	3.402%	$17.1337	$17.13	$17.15	$17.10
Purchase #2	$101.52	5.461%	$107.064	$107.06	$107.05	$107.10
Purchase #3	$164.29	3.407%	$169.8874	$169.89	$169.90	$169.90
Purchase #4	$102.25	6.302%	$108.6938	$108.69	$108.70	$108.70
Purchase #5	$134.77	4.251%	$140.4991	$140.50	$140.50	$140.50
Purchase #6	$164.73	5.553%	$173.8775	$173.88	$173.90	$173.90
Purchase #7	$61.42	9.584%	$67.3065	$67.31	$67.30	$67.30
7 purchase totals =	$745.55		$784.4620	$784.46	$784.50	$784.50