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	$94.80	5.217%	$99.7457	$99.75	$99.75	$99.70
Purchase #2	$34.29	6.711%	$36.5912	$36.59	$36.60	$36.60
Purchase #3	$5.93	12.285%	$6.6585	$6.66	$6.65	$6.70
Purchase #4	$12.30	10.639%	$13.6086	$13.61	$13.60	$13.60
Purchase #5	$134.72	6.254%	$143.1454	$143.15	$143.15	$143.10
Purchase #6	$109.82	10.123%	$120.9371	$120.94	$120.95	$120.90
Purchase #7	$209.92	6.440%	$223.4388	$223.44	$223.45	$223.40
7 purchase totals =	$601.78		$644.1253	$644.14	$644.15	$644.00