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	$51.87	12.129%	$58.1613	$58.16	$58.15	$58.20
Purchase #2	$143.59	3.294%	$148.3199	$148.32	$148.30	$148.30
Purchase #3	$84.94	5.446%	$89.5658	$89.57	$89.55	$89.60
Purchase #4	$139.98	13.619%	$159.0439	$159.04	$159.05	$159.00
Purchase #5	$170.62	9.694%	$187.1599	$187.16	$187.15	$187.20
Purchase #6	$118.29	4.439%	$123.5409	$123.54	$123.55	$123.50
Purchase #7	$76.57	5.296%	$80.6251	$80.63	$80.65	$80.60
7 purchase totals =	$785.86		$846.4168	$846.42	$846.40	$846.40