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	$94.57	4.832%	$99.1396	$99.14	$99.15	$99.10
Purchase #2	$246.56	13.638%	$280.1859	$280.19	$280.20	$280.20
Purchase #3	$180.57	6.723%	$192.7097	$192.71	$192.70	$192.70
Purchase #4	$70.82	7.439%	$76.0883	$76.09	$76.10	$76.10
Purchase #5	$87.96	13.277%	$99.6384	$99.64	$99.65	$99.60
Purchase #6	$105.53	8.680%	$114.69	$114.69	$114.70	$114.70
Purchase #7	$141.33	11.668%	$157.8204	$157.82	$157.80	$157.80
7 purchase totals =	$927.34		$1,020.2723	$1,020.28	$1,020.30	$1,020.20