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	$89.91	7.510%	$96.6622	$96.66	$96.65	$96.70
Purchase #2	$225.46	12.673%	$254.0325	$254.03	$254.05	$254.00
Purchase #3	$91.89	9.762%	$100.8603	$100.86	$100.85	$100.90
Purchase #4	$170.31	3.540%	$176.339	$176.34	$176.35	$176.30
Purchase #5	$52.96	6.222%	$56.2552	$56.26	$56.25	$56.30
Purchase #6	$82.93	8.431%	$89.9218	$89.92	$89.90	$89.90
Purchase #7	$109.29	5.127%	$114.8933	$114.89	$114.90	$114.90
7 purchase totals =	$822.75		$888.9643	$888.96	$888.95	$889.00