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	$16.32	12.447%	$18.3514	$18.35	$18.35	$18.40
Purchase #2	$117.36	6.171%	$124.6023	$124.60	$124.60	$124.60
Purchase #3	$27.81	13.653%	$31.6069	$31.61	$31.60	$31.60
Purchase #4	$103.78	5.608%	$109.6	$109.60	$109.60	$109.60
Purchase #5	$152.83	3.401%	$158.0277	$158.03	$158.05	$158.00
Purchase #6	$18.50	5.301%	$19.4807	$19.48	$19.50	$19.50
Purchase #7	$211.28	8.573%	$229.393	$229.39	$229.40	$229.40
7 purchase totals =	$647.88		$691.0620	$691.06	$691.10	$691.10