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	$168.39	8.834%	$183.2656	$183.27	$183.25	$183.30
Purchase #2	$111.37	10.109%	$122.6284	$122.63	$122.65	$122.60
Purchase #3	$56.41	11.685%	$63.0015	$63.00	$63.00	$63.00
Purchase #4	$92.62	12.240%	$103.9567	$103.96	$103.95	$104.00
Purchase #5	$28.31	10.752%	$31.3539	$31.35	$31.35	$31.40
Purchase #6	$246.90	3.787%	$256.2501	$256.25	$256.25	$256.30
Purchase #7	$91.35	13.699%	$103.864	$103.86	$103.85	$103.90
7 purchase totals =	$795.35		$864.3202	$864.32	$864.30	$864.50