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	$173.33	9.290%	$189.4324	$189.43	$189.45	$189.40
Purchase #2	$78.78	5.122%	$82.8151	$82.82	$82.80	$82.80
Purchase #3	$138.63	4.436%	$144.7796	$144.78	$144.80	$144.80
Purchase #4	$70.36	12.509%	$79.1613	$79.16	$79.15	$79.20
Purchase #5	$189.64	8.343%	$205.4617	$205.46	$205.45	$205.50
Purchase #6	$39.53	6.193%	$41.9781	$41.98	$42.00	$42.00
Purchase #7	$15.30	3.586%	$15.8487	$15.85	$15.85	$15.80
7 purchase totals =	$705.57		$759.4769	$759.48	$759.50	$759.50