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	$141.72	6.413%	$150.8085	$150.81	$150.80	$150.80
Purchase #2	$18.45	3.412%	$19.0795	$19.08	$19.10	$19.10
Purchase #3	$108.83	13.337%	$123.3447	$123.34	$123.35	$123.30
Purchase #4	$135.48	13.589%	$153.8904	$153.89	$153.90	$153.90
Purchase #5	$140.48	6.785%	$150.0116	$150.01	$150.00	$150.00
Purchase #6	$100.34	8.769%	$109.1388	$109.14	$109.15	$109.10
Purchase #7	$34.65	6.173%	$36.7889	$36.79	$36.80	$36.80
7 purchase totals =	$679.95		$743.0624	$743.06	$743.10	$743.00