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	$9.77	5.659%	$10.3229	$10.32	$10.30	$10.30
Purchase #2	$49.74	9.459%	$54.4449	$54.44	$54.45	$54.40
Purchase #3	$74.93	8.299%	$81.1484	$81.15	$81.15	$81.10
Purchase #4	$131.97	6.295%	$140.2775	$140.28	$140.30	$140.30
Purchase #5	$13.84	3.611%	$14.3398	$14.34	$14.35	$14.30
Purchase #6	$231.61	10.459%	$255.8341	$255.83	$255.85	$255.80
Purchase #7	$174.32	12.585%	$196.2582	$196.26	$196.25	$196.30
7 purchase totals =	$686.18		$752.6258	$752.62	$752.65	$752.50