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	$246.44	12.757%	$277.8784	$277.88	$277.90	$277.90
Purchase #2	$99.46	13.204%	$112.5927	$112.59	$112.60	$112.60
Purchase #3	$120.86	6.647%	$128.8936	$128.89	$128.90	$128.90
Purchase #4	$157.92	9.160%	$172.3855	$172.39	$172.40	$172.40
Purchase #5	$36.63	9.176%	$39.9912	$39.99	$40.00	$40.00
Purchase #6	$88.80	9.176%	$96.9483	$96.95	$96.95	$96.90
Purchase #7	$142.59	6.197%	$151.4263	$151.43	$151.45	$151.40
7 purchase totals =	$892.70		$980.1160	$980.12	$980.20	$980.10