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	$97.60	11.643%	$108.9636	$108.96	$108.95	$109.00
Purchase #2	$159.74	7.435%	$171.6167	$171.62	$171.60	$171.60
Purchase #3	$63.48	13.501%	$72.0504	$72.05	$72.05	$72.10
Purchase #4	$169.30	11.122%	$188.1295	$188.13	$188.15	$188.10
Purchase #5	$236.64	4.728%	$247.8283	$247.83	$247.85	$247.80
Purchase #6	$38.84	9.703%	$42.6086	$42.61	$42.60	$42.60
Purchase #7	$95.95	11.695%	$107.1714	$107.17	$107.15	$107.20
7 purchase totals =	$861.55		$938.3685	$938.37	$938.35	$938.40