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	$137.86	12.140%	$154.5962	$154.60	$154.60	$154.60
Purchase #2	$193.55	13.688%	$220.0431	$220.04	$220.05	$220.00
Purchase #3	$156.82	4.666%	$164.1372	$164.14	$164.15	$164.10
Purchase #4	$210.55	4.387%	$219.7868	$219.79	$219.80	$219.80
Purchase #5	$32.71	9.113%	$35.6909	$35.69	$35.70	$35.70
Purchase #6	$38.29	6.395%	$40.7386	$40.74	$40.75	$40.70
Purchase #7	$170.59	8.753%	$185.5217	$185.52	$185.50	$185.50
7 purchase totals =	$940.37		$1,020.5145	$1,020.52	$1,020.55	$1,020.40