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	$141.74	8.572%	$153.89	$153.89	$153.90	$153.90
Purchase #2	$159.37	13.723%	$181.2403	$181.24	$181.25	$181.20
Purchase #3	$31.30	12.630%	$35.2532	$35.25	$35.25	$35.30
Purchase #4	$32.40	5.847%	$34.2944	$34.29	$34.30	$34.30
Purchase #5	$74.81	10.393%	$82.585	$82.59	$82.60	$82.60
Purchase #6	$5.44	9.216%	$5.9414	$5.94	$5.95	$5.90
Purchase #7	$89.33	9.571%	$97.8798	$97.88	$97.90	$97.90
7 purchase totals =	$534.39		$591.0841	$591.08	$591.15	$591.10