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	$90.66	9.473%	$99.2482	$99.25	$99.25	$99.20
Purchase #2	$150.59	7.260%	$161.5228	$161.52	$161.50	$161.50
Purchase #3	$130.61	13.830%	$148.6734	$148.67	$148.65	$148.70
Purchase #4	$50.44	11.483%	$56.232	$56.23	$56.25	$56.20
Purchase #5	$179.55	6.142%	$190.578	$190.58	$190.60	$190.60
Purchase #6	$131.57	7.577%	$141.5391	$141.54	$141.55	$141.50
Purchase #7	$36.54	6.630%	$38.9626	$38.96	$38.95	$39.00
7 purchase totals =	$769.96		$836.7561	$836.75	$836.75	$836.70