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	$118.44	10.429%	$130.7921	$130.79	$130.80	$130.80
Purchase #2	$196.54	3.583%	$203.582	$203.58	$203.60	$203.60
Purchase #3	$234.37	4.827%	$245.683	$245.68	$245.70	$245.70
Purchase #4	$128.83	11.667%	$143.8606	$143.86	$143.85	$143.90
Purchase #5	$78.98	4.451%	$82.4954	$82.50	$82.50	$82.50
Purchase #6	$98.69	4.481%	$103.1123	$103.11	$103.10	$103.10
Purchase #7	$173.57	10.125%	$191.144	$191.14	$191.15	$191.10
7 purchase totals =	$1,029.42		$1,100.6694	$1,100.66	$1,100.70	$1,100.70