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	$209.90	6.318%	$223.1615	$223.16	$223.15	$223.20
Purchase #2	$65.47	11.395%	$72.9303	$72.93	$72.95	$72.90
Purchase #3	$79.84	3.571%	$82.6911	$82.69	$82.70	$82.70
Purchase #4	$206.98	13.351%	$234.6139	$234.61	$234.60	$234.60
Purchase #5	$116.30	4.444%	$121.4684	$121.47	$121.45	$121.50
Purchase #6	$105.36	7.796%	$113.5739	$113.57	$113.55	$113.60
Purchase #7	$10.88	10.731%	$12.0475	$12.05	$12.05	$12.00
7 purchase totals =	$794.73		$860.4866	$860.48	$860.45	$860.50