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	$224.66	13.829%	$255.7282	$255.73	$255.75	$255.70
Purchase #2	$44.53	10.605%	$49.2524	$49.25	$49.25	$49.30
Purchase #3	$114.60	10.237%	$126.3316	$126.33	$126.35	$126.30
Purchase #4	$80.80	11.851%	$90.3756	$90.38	$90.40	$90.40
Purchase #5	$51.51	7.255%	$55.2471	$55.25	$55.25	$55.20
Purchase #6	$193.51	8.137%	$209.2559	$209.26	$209.25	$209.30
Purchase #7	$154.85	6.477%	$164.8796	$164.88	$164.90	$164.90
7 purchase totals =	$864.46		$951.0704	$951.08	$951.15	$951.10