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	$16.69	10.227%	$18.3969	$18.40	$18.40	$18.40
Purchase #2	$78.73	7.776%	$84.852	$84.85	$84.85	$84.90
Purchase #3	$82.51	10.675%	$91.3179	$91.32	$91.30	$91.30
Purchase #4	$211.34	5.262%	$222.4607	$222.46	$222.45	$222.50
Purchase #5	$137.56	5.204%	$144.7186	$144.72	$144.70	$144.70
Purchase #6	$79.54	13.843%	$90.5507	$90.55	$90.55	$90.60
Purchase #7	$138.83	5.273%	$146.1505	$146.15	$146.15	$146.20
7 purchase totals =	$745.20		$798.4473	$798.45	$798.40	$798.60