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	$65.92	10.513%	$72.8502	$72.85	$72.85	$72.90
Purchase #2	$119.89	7.463%	$128.8374	$128.84	$128.85	$128.80
Purchase #3	$160.71	6.725%	$171.5177	$171.52	$171.50	$171.50
Purchase #4	$11.98	9.441%	$13.111	$13.11	$13.10	$13.10
Purchase #5	$32.42	3.797%	$33.651	$33.65	$33.65	$33.70
Purchase #6	$47.94	13.239%	$54.2868	$54.29	$54.30	$54.30
Purchase #7	$175.31	8.196%	$189.6784	$189.68	$189.70	$189.70
7 purchase totals =	$614.17		$663.9325	$663.94	$663.95	$664.00