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	$201.56	5.575%	$212.797	$212.80	$212.80	$212.80
Purchase #2	$117.40	7.800%	$126.5572	$126.56	$126.55	$126.60
Purchase #3	$45.94	6.416%	$48.8875	$48.89	$48.90	$48.90
Purchase #4	$102.47	8.713%	$111.3982	$111.40	$111.40	$111.40
Purchase #5	$205.63	5.330%	$216.5901	$216.59	$216.60	$216.60
Purchase #6	$235.69	8.168%	$254.9412	$254.94	$254.95	$254.90
Purchase #7	$19.48	3.801%	$20.2204	$20.22	$20.20	$20.20
7 purchase totals =	$928.17		$991.3916	$991.40	$991.40	$991.40