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	$136.31	5.388%	$143.6544	$143.65	$143.65	$143.70
Purchase #2	$56.66	7.692%	$61.0183	$61.02	$61.00	$61.00
Purchase #3	$218.83	12.215%	$245.5601	$245.56	$245.55	$245.60
Purchase #4	$86.32	4.618%	$90.3063	$90.31	$90.30	$90.30
Purchase #5	$33.70	8.236%	$36.4755	$36.48	$36.50	$36.50
Purchase #6	$110.52	5.413%	$116.5024	$116.50	$116.50	$116.50
Purchase #7	$139.58	3.652%	$144.6775	$144.68	$144.70	$144.70
7 purchase totals =	$781.92		$838.1945	$838.20	$838.20	$838.30