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	$72.46	7.728%	$78.0597	$78.06	$78.05	$78.10
Purchase #2	$225.63	11.692%	$252.0107	$252.01	$252.00	$252.00
Purchase #3	$86.95	12.400%	$97.7318	$97.73	$97.75	$97.70
Purchase #4	$108.68	7.471%	$116.7995	$116.80	$116.80	$116.80
Purchase #5	$143.71	4.726%	$150.5017	$150.50	$150.50	$150.50
Purchase #6	$90.59	9.829%	$99.4941	$99.49	$99.50	$99.50
Purchase #7	$103.37	11.767%	$115.5335	$115.53	$115.55	$115.50
7 purchase totals =	$831.39		$910.1310	$910.12	$910.15	$910.10