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	$102.83	8.660%	$111.7351	$111.74	$111.75	$111.70
Purchase #2	$246.62	9.697%	$270.5347	$270.53	$270.55	$270.50
Purchase #3	$141.33	6.224%	$150.1264	$150.13	$150.15	$150.10
Purchase #4	$110.48	11.652%	$123.3531	$123.35	$123.35	$123.40
Purchase #5	$64.75	12.616%	$72.9189	$72.92	$72.90	$72.90
Purchase #6	$100.42	12.376%	$112.848	$112.85	$112.85	$112.80
Purchase #7	$27.80	13.466%	$31.5435	$31.54	$31.55	$31.50
7 purchase totals =	$794.23		$873.0597	$873.06	$873.10	$872.90