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	$18.86	6.366%	$20.0606	$20.06	$20.05	$20.10
Purchase #2	$87.55	13.134%	$99.0488	$99.05	$99.05	$99.00
Purchase #3	$9.46	12.459%	$10.6386	$10.64	$10.65	$10.60
Purchase #4	$229.96	3.246%	$237.4245	$237.42	$237.40	$237.40
Purchase #5	$142.97	11.314%	$159.1456	$159.15	$159.15	$159.10
Purchase #6	$65.47	10.138%	$72.1073	$72.11	$72.10	$72.10
Purchase #7	$166.71	11.329%	$185.5966	$185.60	$185.60	$185.60
7 purchase totals =	$720.98		$784.0220	$784.03	$784.00	$783.90