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	$199.98	12.789%	$225.5554	$225.56	$225.55	$225.60
Purchase #2	$128.98	10.748%	$142.8428	$142.84	$142.85	$142.80
Purchase #3	$37.46	8.265%	$40.5561	$40.56	$40.55	$40.60
Purchase #4	$100.61	7.827%	$108.4847	$108.48	$108.50	$108.50
Purchase #5	$27.59	10.297%	$30.4309	$30.43	$30.45	$30.40
Purchase #6	$35.97	3.204%	$37.1225	$37.12	$37.10	$37.10
Purchase #7	$81.97	9.738%	$89.9522	$89.95	$89.95	$90.00
7 purchase totals =	$612.56		$674.9446	$674.94	$674.95	$675.00