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	$8.58	10.386%	$9.4711	$9.47	$9.45	$9.50
Purchase #2	$238.68	7.221%	$255.9151	$255.92	$255.90	$255.90
Purchase #3	$115.57	13.791%	$131.5083	$131.51	$131.50	$131.50
Purchase #4	$5.63	13.803%	$6.4071	$6.41	$6.40	$6.40
Purchase #5	$50.73	5.232%	$53.3842	$53.38	$53.40	$53.40
Purchase #6	$172.60	13.112%	$195.2313	$195.23	$195.25	$195.20
Purchase #7	$83.31	8.455%	$90.3539	$90.35	$90.35	$90.40
7 purchase totals =	$675.10		$742.2710	$742.27	$742.25	$742.30