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	$92.82	9.584%	$101.7159	$101.72	$101.70	$101.70
Purchase #2	$135.30	4.654%	$141.5969	$141.60	$141.60	$141.60
Purchase #3	$154.70	3.351%	$159.884	$159.88	$159.90	$159.90
Purchase #4	$55.93	9.795%	$61.4083	$61.41	$61.40	$61.40
Purchase #5	$76.52	6.277%	$81.3232	$81.32	$81.30	$81.30
Purchase #6	$186.88	9.471%	$204.5794	$204.58	$204.60	$204.60
Purchase #7	$81.49	9.211%	$88.996	$89.00	$89.00	$89.00
7 purchase totals =	$783.64		$839.5037	$839.51	$839.50	$839.50