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	$199.61	5.129%	$209.848	$209.85	$209.85	$209.80
Purchase #2	$123.41	12.776%	$139.1769	$139.18	$139.20	$139.20
Purchase #3	$127.48	6.706%	$136.0288	$136.03	$136.05	$136.00
Purchase #4	$171.76	12.577%	$193.3623	$193.36	$193.35	$193.40
Purchase #5	$55.87	11.491%	$62.29	$62.29	$62.30	$62.30
Purchase #6	$152.52	4.204%	$158.9319	$158.93	$158.95	$158.90
Purchase #7	$20.99	4.224%	$21.8766	$21.88	$21.90	$21.90
7 purchase totals =	$851.64		$921.5145	$921.52	$921.60	$921.50