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	$190.74	13.677%	$216.8275	$216.83	$216.85	$216.80
Purchase #2	$68.99	4.764%	$72.2767	$72.28	$72.30	$72.30
Purchase #3	$202.92	6.160%	$215.4199	$215.42	$215.40	$215.40
Purchase #4	$173.60	8.233%	$187.8925	$187.89	$187.90	$187.90
Purchase #5	$114.96	12.135%	$128.9104	$128.91	$128.90	$128.90
Purchase #6	$35.87	7.433%	$38.5362	$38.54	$38.55	$38.50
Purchase #7	$37.81	5.588%	$39.9228	$39.92	$39.90	$39.90
7 purchase totals =	$824.89		$899.7860	$899.79	$899.80	$899.70