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	$8.64	5.483%	$9.1137	$9.11	$9.10	$9.10
Purchase #2	$224.63	6.468%	$239.1591	$239.16	$239.15	$239.20
Purchase #3	$79.35	12.624%	$89.3671	$89.37	$89.35	$89.40
Purchase #4	$94.43	12.102%	$105.8579	$105.86	$105.85	$105.90
Purchase #5	$102.44	13.478%	$116.2469	$116.25	$116.25	$116.20
Purchase #6	$131.69	12.832%	$148.5885	$148.59	$148.60	$148.60
Purchase #7	$70.35	3.456%	$72.7813	$72.78	$72.80	$72.80
7 purchase totals =	$711.53		$781.1145	$781.12	$781.10	$781.20