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	$27.37	13.468%	$31.0562	$31.06	$31.05	$31.10
Purchase #2	$38.26	9.799%	$42.0091	$42.01	$42.00	$42.00
Purchase #3	$52.74	5.829%	$55.8142	$55.81	$55.80	$55.80
Purchase #4	$167.32	4.833%	$175.4066	$175.41	$175.40	$175.40
Purchase #5	$12.47	6.109%	$13.2318	$13.23	$13.25	$13.20
Purchase #6	$231.25	12.302%	$259.6984	$259.70	$259.70	$259.70
Purchase #7	$31.81	4.491%	$33.2386	$33.24	$33.25	$33.20
7 purchase totals =	$561.22		$610.4549	$610.46	$610.45	$610.40