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	$154.83	8.211%	$167.5431	$167.54	$167.55	$167.50
Purchase #2	$48.34	3.460%	$50.0126	$50.01	$50.00	$50.00
Purchase #3	$241.75	3.439%	$250.0638	$250.06	$250.05	$250.10
Purchase #4	$241.31	9.233%	$263.5902	$263.59	$263.60	$263.60
Purchase #5	$7.28	3.504%	$7.5351	$7.54	$7.55	$7.50
Purchase #6	$37.51	7.712%	$40.4028	$40.40	$40.40	$40.40
Purchase #7	$34.30	9.154%	$37.4398	$37.44	$37.45	$37.40
7 purchase totals =	$765.32		$816.5874	$816.58	$816.60	$816.50