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	$170.72	12.398%	$191.8859	$191.89	$191.90	$191.90
Purchase #2	$242.55	6.384%	$258.0344	$258.03	$258.05	$258.00
Purchase #3	$132.36	12.206%	$148.5159	$148.52	$148.50	$148.50
Purchase #4	$247.35	3.327%	$255.5793	$255.58	$255.60	$255.60
Purchase #5	$89.74	11.425%	$99.9928	$99.99	$100.00	$100.00
Purchase #6	$170.58	12.474%	$191.8581	$191.86	$191.85	$191.90
Purchase #7	$244.31	11.654%	$272.7819	$272.78	$272.80	$272.80
7 purchase totals =	$1,297.61		$1,418.6483	$1,418.65	$1,418.70	$1,418.70