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	$141.68	6.140%	$150.3792	$150.38	$150.40	$150.40
Purchase #2	$166.48	10.201%	$183.4626	$183.46	$183.45	$183.50
Purchase #3	$208.85	12.689%	$235.351	$235.35	$235.35	$235.40
Purchase #4	$54.95	3.217%	$56.7177	$56.72	$56.70	$56.70
Purchase #5	$160.78	3.397%	$166.2417	$166.24	$166.25	$166.20
Purchase #6	$135.49	13.520%	$153.8082	$153.81	$153.80	$153.80
Purchase #7	$134.83	8.206%	$145.8941	$145.89	$145.90	$145.90
7 purchase totals =	$1,003.06		$1,091.8545	$1,091.85	$1,091.85	$1,091.90