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	$67.74	6.290%	$72.0008	$72.00	$72.00	$72.00
Purchase #2	$49.70	7.840%	$53.5965	$53.60	$53.60	$53.60
Purchase #3	$136.28	10.380%	$150.4259	$150.43	$150.45	$150.40
Purchase #4	$93.39	12.263%	$104.8424	$104.84	$104.85	$104.80
Purchase #5	$20.92	11.508%	$23.3275	$23.33	$23.35	$23.30
Purchase #6	$144.37	12.836%	$162.9013	$162.90	$162.90	$162.90
Purchase #7	$153.27	13.404%	$173.8143	$173.81	$173.80	$173.80
7 purchase totals =	$665.67		$740.9087	$740.91	$740.95	$740.80