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	$49.42	12.477%	$55.5861	$55.59	$55.60	$55.60
Purchase #2	$19.50	13.625%	$22.1569	$22.16	$22.15	$22.20
Purchase #3	$206.34	6.357%	$219.457	$219.46	$219.45	$219.50
Purchase #4	$16.37	11.682%	$18.2823	$18.28	$18.30	$18.30
Purchase #5	$5.86	6.465%	$6.2388	$6.24	$6.25	$6.20
Purchase #6	$83.81	6.786%	$89.4973	$89.50	$89.50	$89.50
Purchase #7	$80.25	11.181%	$89.2228	$89.22	$89.20	$89.20
7 purchase totals =	$461.55		$500.4412	$500.45	$500.45	$500.50