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	$68.43	4.676%	$71.6298	$71.63	$71.65	$71.60
Purchase #2	$51.93	3.584%	$53.7912	$53.79	$53.80	$53.80
Purchase #3	$179.78	6.114%	$190.7717	$190.77	$190.75	$190.80
Purchase #4	$148.89	10.709%	$164.8346	$164.83	$164.85	$164.80
Purchase #5	$68.47	5.425%	$72.1845	$72.18	$72.20	$72.20
Purchase #6	$192.53	13.785%	$219.0703	$219.07	$219.05	$219.10
Purchase #7	$43.63	11.819%	$48.7866	$48.79	$48.80	$48.80
7 purchase totals =	$753.66		$821.0687	$821.06	$821.10	$821.10