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	$64.77	6.332%	$68.8712	$68.87	$68.85	$68.90
Purchase #2	$181.33	9.823%	$199.142	$199.14	$199.15	$199.10
Purchase #3	$100.51	10.457%	$111.0203	$111.02	$111.00	$111.00
Purchase #4	$76.62	7.844%	$82.6301	$82.63	$82.65	$82.60
Purchase #5	$33.41	6.568%	$35.6044	$35.60	$35.60	$35.60
Purchase #6	$68.35	7.470%	$73.4557	$73.46	$73.45	$73.50
Purchase #7	$97.97	6.624%	$104.4595	$104.46	$104.45	$104.50
7 purchase totals =	$622.96		$675.1832	$675.18	$675.15	$675.20