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	$246.32	13.243%	$278.9402	$278.94	$278.95	$278.90
Purchase #2	$95.67	10.753%	$105.9574	$105.96	$105.95	$106.00
Purchase #3	$56.97	5.871%	$60.3147	$60.31	$60.30	$60.30
Purchase #4	$222.78	11.234%	$247.8071	$247.81	$247.80	$247.80
Purchase #5	$44.31	7.177%	$47.4901	$47.49	$47.50	$47.50
Purchase #6	$55.58	7.153%	$59.5556	$59.56	$59.55	$59.60
Purchase #7	$53.90	13.821%	$61.3495	$61.35	$61.35	$61.30
7 purchase totals =	$775.53		$861.4146	$861.42	$861.40	$861.40