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	$208.36	10.772%	$230.8045	$230.80	$230.80	$230.80
Purchase #2	$82.63	4.760%	$86.5632	$86.56	$86.55	$86.60
Purchase #3	$160.27	9.477%	$175.4588	$175.46	$175.45	$175.50
Purchase #4	$185.91	5.219%	$195.6126	$195.61	$195.60	$195.60
Purchase #5	$126.36	13.410%	$143.3049	$143.30	$143.30	$143.30
Purchase #6	$104.52	6.525%	$111.3399	$111.34	$111.35	$111.30
Purchase #7	$170.89	4.651%	$178.8381	$178.84	$178.85	$178.80
7 purchase totals =	$1,038.94		$1,121.9220	$1,121.91	$1,121.90	$1,121.90