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	$155.78	9.683%	$170.8642	$170.86	$170.85	$170.90
Purchase #2	$94.99	8.698%	$103.2522	$103.25	$103.25	$103.30
Purchase #3	$235.36	10.597%	$260.3011	$260.30	$260.30	$260.30
Purchase #4	$72.91	12.759%	$82.2126	$82.21	$82.20	$82.20
Purchase #5	$187.88	12.158%	$210.7225	$210.72	$210.70	$210.70
Purchase #6	$178.56	6.715%	$190.5503	$190.55	$190.55	$190.60
Purchase #7	$120.97	13.844%	$137.7171	$137.72	$137.70	$137.70
7 purchase totals =	$1,046.45		$1,155.6200	$1,155.61	$1,155.55	$1,155.70