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	$169.39	12.143%	$189.959	$189.96	$189.95	$190.00
Purchase #2	$151.80	10.790%	$168.1792	$168.18	$168.20	$168.20
Purchase #3	$157.27	3.394%	$162.6077	$162.61	$162.60	$162.60
Purchase #4	$49.48	4.837%	$51.8733	$51.87	$51.85	$51.90
Purchase #5	$60.76	9.470%	$66.514	$66.51	$66.50	$66.50
Purchase #6	$231.30	4.838%	$242.4903	$242.49	$242.50	$242.50
Purchase #7	$35.83	3.473%	$37.0744	$37.07	$37.05	$37.10
7 purchase totals =	$855.83		$918.6979	$918.69	$918.65	$918.80