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	$9.56	12.653%	$10.7696	$10.77	$10.75	$10.80
Purchase #2	$13.70	4.793%	$14.3566	$14.36	$14.35	$14.40
Purchase #3	$36.47	8.513%	$39.5747	$39.57	$39.55	$39.60
Purchase #4	$55.63	6.221%	$59.0907	$59.09	$59.10	$59.10
Purchase #5	$87.43	12.247%	$98.1376	$98.14	$98.15	$98.10
Purchase #6	$53.79	3.755%	$55.8098	$55.81	$55.80	$55.80
Purchase #7	$87.32	3.864%	$90.694	$90.69	$90.70	$90.70
7 purchase totals =	$343.90		$368.4330	$368.43	$368.40	$368.50