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	$103.40	7.698%	$111.3597	$111.36	$111.35	$111.40
Purchase #2	$37.94	4.282%	$39.5646	$39.56	$39.55	$39.60
Purchase #3	$66.51	8.341%	$72.0576	$72.06	$72.05	$72.10
Purchase #4	$29.95	11.220%	$33.3104	$33.31	$33.30	$33.30
Purchase #5	$167.42	13.755%	$190.4486	$190.45	$190.45	$190.40
Purchase #6	$104.66	11.549%	$116.7472	$116.75	$116.75	$116.70
Purchase #7	$75.80	4.785%	$79.427	$79.43	$79.45	$79.40
7 purchase totals =	$585.68		$642.9151	$642.92	$642.90	$642.90