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	$170.94	9.298%	$186.834	$186.83	$186.85	$186.80
Purchase #2	$117.86	12.638%	$132.7551	$132.76	$132.75	$132.80
Purchase #3	$86.47	6.693%	$92.2574	$92.26	$92.25	$92.30
Purchase #4	$247.52	9.411%	$270.8141	$270.81	$270.80	$270.80
Purchase #5	$249.77	5.855%	$264.394	$264.39	$264.40	$264.40
Purchase #6	$200.64	12.394%	$225.5073	$225.51	$225.50	$225.50
Purchase #7	$30.80	6.662%	$32.8519	$32.85	$32.85	$32.90
7 purchase totals =	$1,104.00		$1,205.4138	$1,205.41	$1,205.40	$1,205.50