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	$69.78	3.460%	$72.1944	$72.19	$72.20	$72.20
Purchase #2	$37.87	12.852%	$42.7371	$42.74	$42.75	$42.70
Purchase #3	$19.38	8.293%	$20.9872	$20.99	$21.00	$21.00
Purchase #4	$38.87	12.749%	$43.8255	$43.83	$43.85	$43.80
Purchase #5	$82.53	12.263%	$92.6507	$92.65	$92.65	$92.70
Purchase #6	$241.98	3.395%	$250.1952	$250.20	$250.20	$250.20
Purchase #7	$94.37	6.586%	$100.5852	$100.59	$100.60	$100.60
7 purchase totals =	$584.78		$623.1753	$623.19	$623.25	$623.20