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	$38.89	8.697%	$42.2723	$42.27	$42.25	$42.30
Purchase #2	$6.44	11.166%	$7.1591	$7.16	$7.15	$7.20
Purchase #3	$140.78	4.296%	$146.8279	$146.83	$146.85	$146.80
Purchase #4	$173.72	4.299%	$181.1882	$181.19	$181.20	$181.20
Purchase #5	$161.42	11.794%	$180.4579	$180.46	$180.45	$180.50
Purchase #6	$199.35	12.679%	$224.6256	$224.63	$224.65	$224.60
Purchase #7	$71.86	11.183%	$79.8961	$79.90	$79.90	$79.90
7 purchase totals =	$792.46		$862.4271	$862.44	$862.45	$862.50