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	$20.66	3.391%	$21.3606	$21.36	$21.35	$21.40
Purchase #2	$85.87	5.846%	$90.89	$90.89	$90.90	$90.90
Purchase #3	$207.75	3.638%	$215.3079	$215.31	$215.30	$215.30
Purchase #4	$54.36	13.104%	$61.4833	$61.48	$61.50	$61.50
Purchase #5	$85.99	8.864%	$93.6122	$93.61	$93.60	$93.60
Purchase #6	$83.47	10.715%	$92.4138	$92.41	$92.40	$92.40
Purchase #7	$74.71	8.165%	$80.8101	$80.81	$80.80	$80.80
7 purchase totals =	$612.81		$655.8779	$655.87	$655.85	$655.90