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	$56.32	5.833%	$59.6051	$59.61	$59.60	$59.60
Purchase #2	$108.53	12.469%	$122.0626	$122.06	$122.05	$122.10
Purchase #3	$96.76	9.585%	$106.0344	$106.03	$106.05	$106.00
Purchase #4	$176.30	13.673%	$200.4055	$200.41	$200.40	$200.40
Purchase #5	$207.43	10.564%	$229.3429	$229.34	$229.35	$229.30
Purchase #6	$199.33	3.307%	$205.9218	$205.92	$205.90	$205.90
Purchase #7	$65.57	10.859%	$72.6902	$72.69	$72.70	$72.70
7 purchase totals =	$910.24		$996.0625	$996.06	$996.05	$996.00