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	$98.44	10.611%	$108.8855	$108.89	$108.90	$108.90
Purchase #2	$29.51	8.159%	$31.9177	$31.92	$31.90	$31.90
Purchase #3	$88.43	5.516%	$93.3078	$93.31	$93.30	$93.30
Purchase #4	$29.51	9.463%	$32.3025	$32.30	$32.30	$32.30
Purchase #5	$81.60	13.805%	$92.8649	$92.86	$92.85	$92.90
Purchase #6	$57.38	9.218%	$62.6693	$62.67	$62.65	$62.70
Purchase #7	$183.43	8.747%	$199.4746	$199.47	$199.45	$199.50
7 purchase totals =	$568.30		$621.4223	$621.42	$621.35	$621.50