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	$38.86	8.401%	$42.1246	$42.12	$42.10	$42.10
Purchase #2	$41.69	7.225%	$44.7021	$44.70	$44.70	$44.70
Purchase #3	$118.53	11.191%	$131.7947	$131.79	$131.80	$131.80
Purchase #4	$122.94	6.813%	$131.3159	$131.32	$131.30	$131.30
Purchase #5	$224.77	12.551%	$252.9809	$252.98	$253.00	$253.00
Purchase #6	$128.58	4.844%	$134.8084	$134.81	$134.80	$134.80
Purchase #7	$181.27	8.526%	$196.7251	$196.73	$196.75	$196.70
7 purchase totals =	$856.64		$934.4517	$934.45	$934.45	$934.40