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	$59.86	13.234%	$67.7819	$67.78	$67.80	$67.80
Purchase #2	$40.90	11.238%	$45.4963	$45.50	$45.50	$45.50
Purchase #3	$158.84	6.700%	$169.4823	$169.48	$169.50	$169.50
Purchase #4	$123.82	10.851%	$137.2557	$137.26	$137.25	$137.30
Purchase #5	$242.52	6.406%	$258.0558	$258.06	$258.05	$258.10
Purchase #6	$15.37	4.531%	$16.0664	$16.07	$16.05	$16.10
Purchase #7	$157.61	4.758%	$165.1091	$165.11	$165.10	$165.10
7 purchase totals =	$798.92		$859.2475	$859.26	$859.25	$859.40