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	$83.89	9.450%	$91.8176	$91.82	$91.80	$91.80
Purchase #2	$151.58	8.547%	$164.5355	$164.54	$164.55	$164.50
Purchase #3	$119.31	7.106%	$127.7882	$127.79	$127.80	$127.80
Purchase #4	$123.99	5.519%	$130.833	$130.83	$130.85	$130.80
Purchase #5	$32.33	3.719%	$33.5324	$33.53	$33.55	$33.50
Purchase #6	$91.90	9.183%	$100.3392	$100.34	$100.35	$100.30
Purchase #7	$119.47	9.692%	$131.049	$131.05	$131.05	$131.00
7 purchase totals =	$722.47		$779.8949	$779.90	$779.95	$779.70