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	$39.87	7.428%	$42.8315	$42.83	$42.85	$42.80
Purchase #2	$190.37	13.515%	$216.0985	$216.10	$216.10	$216.10
Purchase #3	$228.56	8.232%	$247.3751	$247.38	$247.40	$247.40
Purchase #4	$196.71	4.352%	$205.2708	$205.27	$205.25	$205.30
Purchase #5	$126.36	10.737%	$139.9273	$139.93	$139.95	$139.90
Purchase #6	$34.57	11.249%	$38.4588	$38.46	$38.45	$38.50
Purchase #7	$90.42	10.555%	$99.9638	$99.96	$99.95	$100.00
7 purchase totals =	$906.86		$989.9258	$989.93	$989.95	$990.00