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	$7.77	6.378%	$8.2656	$8.27	$8.25	$8.30
Purchase #2	$144.93	9.218%	$158.2896	$158.29	$158.30	$158.30
Purchase #3	$211.71	6.766%	$226.0343	$226.03	$226.05	$226.00
Purchase #4	$246.54	7.427%	$264.8505	$264.85	$264.85	$264.90
Purchase #5	$115.39	13.184%	$130.603	$130.60	$130.60	$130.60
Purchase #6	$85.37	4.621%	$89.3149	$89.31	$89.30	$89.30
Purchase #7	$199.85	9.151%	$218.1383	$218.14	$218.15	$218.10
7 purchase totals =	$1,011.56		$1,095.4962	$1,095.49	$1,095.50	$1,095.50