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	$169.90	11.105%	$188.7674	$188.77	$188.75	$188.80
Purchase #2	$126.32	10.364%	$139.4118	$139.41	$139.40	$139.40
Purchase #3	$167.38	5.460%	$176.5189	$176.52	$176.50	$176.50
Purchase #4	$224.25	7.785%	$241.7079	$241.71	$241.70	$241.70
Purchase #5	$71.95	8.827%	$78.301	$78.30	$78.30	$78.30
Purchase #6	$96.68	4.814%	$101.3342	$101.33	$101.35	$101.30
Purchase #7	$30.84	6.642%	$32.8884	$32.89	$32.90	$32.90
7 purchase totals =	$887.32		$958.9296	$958.93	$958.90	$958.90