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	$65.61	12.516%	$73.8217	$73.82	$73.80	$73.80
Purchase #2	$46.41	4.351%	$48.4293	$48.43	$48.45	$48.40
Purchase #3	$89.49	10.652%	$99.0225	$99.02	$99.00	$99.00
Purchase #4	$10.84	4.380%	$11.3148	$11.31	$11.30	$11.30
Purchase #5	$22.52	12.183%	$25.2636	$25.26	$25.25	$25.30
Purchase #6	$144.67	13.591%	$164.3321	$164.33	$164.35	$164.30
Purchase #7	$141.90	3.317%	$146.6068	$146.61	$146.60	$146.60
7 purchase totals =	$521.44		$568.7908	$568.78	$568.75	$568.70