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	$88.52	12.605%	$99.6779	$99.68	$99.70	$99.70
Purchase #2	$139.57	7.787%	$150.4383	$150.44	$150.45	$150.40
Purchase #3	$240.33	13.161%	$271.9598	$271.96	$271.95	$272.00
Purchase #4	$101.80	3.233%	$105.0912	$105.09	$105.10	$105.10
Purchase #5	$128.87	13.861%	$146.7327	$146.73	$146.75	$146.70
Purchase #6	$81.30	11.160%	$90.3731	$90.37	$90.35	$90.40
Purchase #7	$209.71	4.820%	$219.818	$219.82	$219.80	$219.80
7 purchase totals =	$990.10		$1,084.0910	$1,084.09	$1,084.10	$1,084.10