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	$211.68	13.808%	$240.9088	$240.91	$240.90	$240.90
Purchase #2	$58.71	8.696%	$63.8154	$63.82	$63.80	$63.80
Purchase #3	$106.77	9.369%	$116.7733	$116.77	$116.75	$116.80
Purchase #4	$82.94	7.754%	$89.3712	$89.37	$89.35	$89.40
Purchase #5	$91.72	10.153%	$101.0323	$101.03	$101.05	$101.00
Purchase #6	$115.54	12.630%	$130.1327	$130.13	$130.15	$130.10
Purchase #7	$212.66	10.278%	$234.5172	$234.52	$234.50	$234.50
7 purchase totals =	$880.02		$976.5509	$976.55	$976.50	$976.50