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	$29.25	6.774%	$31.2314	$31.23	$31.25	$31.20
Purchase #2	$93.93	9.317%	$102.6815	$102.68	$102.70	$102.70
Purchase #3	$249.73	3.431%	$258.2982	$258.30	$258.30	$258.30
Purchase #4	$20.79	5.339%	$21.9	$21.90	$21.90	$21.90
Purchase #5	$79.93	11.728%	$89.3042	$89.30	$89.30	$89.30
Purchase #6	$69.41	6.636%	$74.016	$74.02	$74.00	$74.00
Purchase #7	$175.50	11.685%	$196.0072	$196.01	$196.00	$196.00
7 purchase totals =	$718.54		$773.4385	$773.44	$773.45	$773.40