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	$18.58	10.582%	$20.5461	$20.55	$20.55	$20.50
Purchase #2	$45.59	12.280%	$51.1885	$51.19	$51.20	$51.20
Purchase #3	$247.34	11.848%	$276.6448	$276.64	$276.65	$276.60
Purchase #4	$106.27	4.503%	$111.0553	$111.06	$111.05	$111.10
Purchase #5	$8.84	12.263%	$9.924	$9.92	$9.90	$9.90
Purchase #6	$100.25	5.193%	$105.456	$105.46	$105.45	$105.50
Purchase #7	$39.43	6.378%	$41.9448	$41.94	$41.95	$41.90
7 purchase totals =	$566.30		$616.7595	$616.76	$616.75	$616.70