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	$25.46	13.282%	$28.8416	$28.84	$28.85	$28.80
Purchase #2	$116.39	11.370%	$129.6235	$129.62	$129.60	$129.60
Purchase #3	$104.72	5.549%	$110.5309	$110.53	$110.55	$110.50
Purchase #4	$101.52	9.735%	$111.403	$111.40	$111.40	$111.40
Purchase #5	$71.48	9.763%	$78.4586	$78.46	$78.45	$78.50
Purchase #6	$247.97	12.841%	$279.8118	$279.81	$279.80	$279.80
Purchase #7	$117.32	6.381%	$124.8062	$124.81	$124.80	$124.80
7 purchase totals =	$784.86		$863.4756	$863.47	$863.45	$863.40