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	$83.41	5.542%	$88.0326	$88.03	$88.05	$88.00
Purchase #2	$80.83	8.255%	$87.5025	$87.50	$87.50	$87.50
Purchase #3	$157.46	13.336%	$178.4589	$178.46	$178.45	$178.50
Purchase #4	$33.93	3.367%	$35.0724	$35.07	$35.05	$35.10
Purchase #5	$144.30	7.179%	$154.6593	$154.66	$154.65	$154.70
Purchase #6	$82.35	10.443%	$90.9498	$90.95	$90.95	$90.90
Purchase #7	$14.63	3.604%	$15.1573	$15.16	$15.15	$15.20
7 purchase totals =	$596.91		$649.8328	$649.83	$649.80	$649.90