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	$88.39	13.309%	$100.1538	$100.15	$100.15	$100.20
Purchase #2	$227.97	6.599%	$243.0137	$243.01	$243.00	$243.00
Purchase #3	$212.94	9.447%	$233.0564	$233.06	$233.05	$233.10
Purchase #4	$18.34	6.233%	$19.4831	$19.48	$19.50	$19.50
Purchase #5	$86.83	9.124%	$94.7524	$94.75	$94.75	$94.80
Purchase #6	$58.86	13.654%	$66.8967	$66.90	$66.90	$66.90
Purchase #7	$126.28	13.191%	$142.9376	$142.94	$142.95	$142.90
7 purchase totals =	$819.61		$900.2937	$900.29	$900.30	$900.40