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	$72.44	13.576%	$82.2745	$82.27	$82.25	$82.30
Purchase #2	$240.69	11.141%	$267.5053	$267.51	$267.50	$267.50
Purchase #3	$100.67	8.704%	$109.4323	$109.43	$109.45	$109.40
Purchase #4	$105.43	8.431%	$114.3188	$114.32	$114.30	$114.30
Purchase #5	$43.96	6.319%	$46.7378	$46.74	$46.75	$46.70
Purchase #6	$157.90	5.368%	$166.3761	$166.38	$166.40	$166.40
Purchase #7	$120.94	7.713%	$130.2681	$130.27	$130.25	$130.30
7 purchase totals =	$842.03		$916.9129	$916.92	$916.90	$916.90