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	$159.34	7.213%	$170.8332	$170.83	$170.85	$170.80
Purchase #2	$83.56	10.227%	$92.1057	$92.11	$92.10	$92.10
Purchase #3	$178.71	12.400%	$200.87	$200.87	$200.85	$200.90
Purchase #4	$212.61	9.770%	$233.382	$233.38	$233.40	$233.40
Purchase #5	$122.33	13.126%	$138.387	$138.39	$138.40	$138.40
Purchase #6	$187.47	5.814%	$198.3695	$198.37	$198.35	$198.40
Purchase #7	$173.80	8.312%	$188.2463	$188.25	$188.25	$188.20
7 purchase totals =	$1,117.82		$1,222.1937	$1,222.20	$1,222.20	$1,222.20