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	$28.25	6.407%	$30.06	$30.06	$30.05	$30.10
Purchase #2	$63.85	10.465%	$70.5319	$70.53	$70.55	$70.50
Purchase #3	$138.59	12.431%	$155.8181	$155.82	$155.80	$155.80
Purchase #4	$173.88	8.333%	$188.3694	$188.37	$188.35	$188.40
Purchase #5	$18.89	3.457%	$19.543	$19.54	$19.55	$19.50
Purchase #6	$19.56	4.638%	$20.4672	$20.47	$20.45	$20.50
Purchase #7	$67.63	9.164%	$73.8276	$73.83	$73.85	$73.80
7 purchase totals =	$510.65		$558.6172	$558.62	$558.60	$558.60