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	$136.49	12.558%	$153.6304	$153.63	$153.65	$153.60
Purchase #2	$141.94	6.295%	$150.8751	$150.88	$150.90	$150.90
Purchase #3	$192.33	7.547%	$206.8451	$206.85	$206.85	$206.80
Purchase #4	$96.31	12.104%	$107.9674	$107.97	$107.95	$108.00
Purchase #5	$73.57	7.169%	$78.8442	$78.84	$78.85	$78.80
Purchase #6	$11.61	10.816%	$12.8657	$12.87	$12.85	$12.90
Purchase #7	$182.52	3.856%	$189.558	$189.56	$189.55	$189.60
7 purchase totals =	$834.77		$900.5859	$900.60	$900.60	$900.60