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	$70.34	3.270%	$72.6401	$72.64	$72.65	$72.60
Purchase #2	$70.46	3.411%	$72.8634	$72.86	$72.85	$72.90
Purchase #3	$104.62	5.201%	$110.0613	$110.06	$110.05	$110.10
Purchase #4	$67.91	8.640%	$73.7774	$73.78	$73.80	$73.80
Purchase #5	$10.37	10.245%	$11.4324	$11.43	$11.45	$11.40
Purchase #6	$15.57	4.643%	$16.2929	$16.29	$16.30	$16.30
Purchase #7	$131.34	9.117%	$143.3143	$143.31	$143.30	$143.30
7 purchase totals =	$470.61		$500.3818	$500.37	$500.40	$500.40