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	$32.45	13.393%	$36.796	$36.80	$36.80	$36.80
Purchase #2	$159.88	5.630%	$168.8812	$168.88	$168.90	$168.90
Purchase #3	$182.98	4.712%	$191.602	$191.60	$191.60	$191.60
Purchase #4	$80.96	5.570%	$85.4695	$85.47	$85.45	$85.50
Purchase #5	$233.70	5.196%	$245.8431	$245.84	$245.85	$245.80
Purchase #6	$10.87	12.825%	$12.2641	$12.26	$12.25	$12.30
Purchase #7	$95.68	5.861%	$101.2878	$101.29	$101.30	$101.30
7 purchase totals =	$796.52		$842.1437	$842.14	$842.15	$842.20