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	$55.48	3.459%	$57.3991	$57.40	$57.40	$57.40
Purchase #2	$160.61	11.117%	$178.465	$178.47	$178.45	$178.50
Purchase #3	$55.82	6.137%	$59.2457	$59.25	$59.25	$59.20
Purchase #4	$190.95	3.762%	$198.1335	$198.13	$198.15	$198.10
Purchase #5	$41.98	5.155%	$44.1441	$44.14	$44.15	$44.10
Purchase #6	$233.25	6.559%	$248.5489	$248.55	$248.55	$248.50
Purchase #7	$10.80	13.348%	$12.2416	$12.24	$12.25	$12.20
7 purchase totals =	$748.89		$798.1779	$798.18	$798.20	$798.00