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	$155.41	11.790%	$173.7328	$173.73	$173.75	$173.70
Purchase #2	$174.66	13.546%	$198.3194	$198.32	$198.30	$198.30
Purchase #3	$76.96	7.755%	$82.9282	$82.93	$82.95	$82.90
Purchase #4	$94.35	4.133%	$98.2495	$98.25	$98.25	$98.20
Purchase #5	$145.97	11.172%	$162.2778	$162.28	$162.30	$162.30
Purchase #6	$80.64	12.197%	$90.4757	$90.48	$90.50	$90.50
Purchase #7	$212.60	10.253%	$234.3979	$234.40	$234.40	$234.40
7 purchase totals =	$940.59		$1,040.3813	$1,040.39	$1,040.45	$1,040.30