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	$7.33	6.451%	$7.8029	$7.80	$7.80	$7.80
Purchase #2	$212.65	3.403%	$219.8865	$219.89	$219.90	$219.90
Purchase #3	$127.52	12.190%	$143.0647	$143.06	$143.05	$143.10
Purchase #4	$106.31	11.131%	$118.1434	$118.14	$118.15	$118.10
Purchase #5	$121.79	5.190%	$128.1109	$128.11	$128.10	$128.10
Purchase #6	$134.41	5.826%	$142.2407	$142.24	$142.25	$142.20
Purchase #7	$215.80	5.740%	$228.1869	$228.19	$228.20	$228.20
7 purchase totals =	$925.81		$987.4360	$987.43	$987.45	$987.40