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	$26.44	9.329%	$28.9066	$28.91	$28.90	$28.90
Purchase #2	$168.96	9.457%	$184.9385	$184.94	$184.95	$184.90
Purchase #3	$105.69	6.435%	$112.4912	$112.49	$112.50	$112.50
Purchase #4	$150.87	4.738%	$158.0182	$158.02	$158.00	$158.00
Purchase #5	$149.62	4.448%	$156.2751	$156.28	$156.30	$156.30
Purchase #6	$95.59	4.649%	$100.034	$100.03	$100.05	$100.00
Purchase #7	$76.42	13.788%	$86.9568	$86.96	$86.95	$87.00
7 purchase totals =	$773.59		$827.6204	$827.63	$827.65	$827.60