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	$125.54	4.441%	$131.1152	$131.12	$131.10	$131.10
Purchase #2	$59.94	10.865%	$66.4525	$66.45	$66.45	$66.50
Purchase #3	$59.68	13.415%	$67.6861	$67.69	$67.70	$67.70
Purchase #4	$181.32	3.365%	$187.4214	$187.42	$187.40	$187.40
Purchase #5	$14.29	5.209%	$15.0344	$15.03	$15.05	$15.00
Purchase #6	$84.27	12.540%	$94.8375	$94.84	$94.85	$94.80
Purchase #7	$35.61	12.171%	$39.9441	$39.94	$39.95	$39.90
7 purchase totals =	$560.65		$602.4912	$602.49	$602.50	$602.40