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	$172.51	12.347%	$193.8098	$193.81	$193.80	$193.80
Purchase #2	$81.52	10.711%	$90.2516	$90.25	$90.25	$90.30
Purchase #3	$41.89	11.747%	$46.8108	$46.81	$46.80	$46.80
Purchase #4	$110.32	9.532%	$120.8357	$120.84	$120.85	$120.80
Purchase #5	$93.85	9.667%	$102.9225	$102.92	$102.90	$102.90
Purchase #6	$27.64	8.104%	$29.8799	$29.88	$29.90	$29.90
Purchase #7	$45.51	13.729%	$51.7581	$51.76	$51.75	$51.80
7 purchase totals =	$573.24		$636.2684	$636.27	$636.25	$636.30