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	$206.43	5.714%	$218.2254	$218.23	$218.25	$218.20
Purchase #2	$164.92	4.825%	$172.8774	$172.88	$172.90	$172.90
Purchase #3	$64.85	4.130%	$67.5283	$67.53	$67.55	$67.50
Purchase #4	$27.60	10.260%	$30.4318	$30.43	$30.45	$30.40
Purchase #5	$174.97	13.669%	$198.8866	$198.89	$198.90	$198.90
Purchase #6	$226.36	6.600%	$241.2998	$241.30	$241.30	$241.30
Purchase #7	$60.92	10.207%	$67.1381	$67.14	$67.15	$67.10
7 purchase totals =	$926.05		$996.3874	$996.40	$996.50	$996.30