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	$66.96	6.387%	$71.2367	$71.24	$71.25	$71.20
Purchase #2	$90.27	4.397%	$94.2392	$94.24	$94.25	$94.20
Purchase #3	$183.90	13.505%	$208.7357	$208.74	$208.75	$208.70
Purchase #4	$102.40	11.134%	$113.8012	$113.80	$113.80	$113.80
Purchase #5	$143.48	5.626%	$151.5522	$151.55	$151.55	$151.60
Purchase #6	$77.31	6.112%	$82.0352	$82.04	$82.05	$82.00
Purchase #7	$151.60	13.550%	$172.1418	$172.14	$172.15	$172.10
7 purchase totals =	$815.92		$893.7420	$893.75	$893.80	$893.60