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	$157.79	8.828%	$171.7197	$171.72	$171.70	$171.70
Purchase #2	$37.76	3.447%	$39.0616	$39.06	$39.05	$39.10
Purchase #3	$200.54	12.614%	$225.8361	$225.84	$225.85	$225.80
Purchase #4	$19.80	9.102%	$21.6022	$21.60	$21.60	$21.60
Purchase #5	$102.63	5.290%	$108.0591	$108.06	$108.05	$108.10
Purchase #6	$99.96	4.644%	$104.6021	$104.60	$104.60	$104.60
Purchase #7	$158.89	5.407%	$167.4812	$167.48	$167.50	$167.50
7 purchase totals =	$777.37		$838.3620	$838.36	$838.35	$838.40