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	$173.26	10.332%	$191.1612	$191.16	$191.15	$191.20
Purchase #2	$95.68	4.483%	$99.9693	$99.97	$99.95	$100.00
Purchase #3	$69.85	3.724%	$72.4512	$72.45	$72.45	$72.50
Purchase #4	$39.48	8.765%	$42.9404	$42.94	$42.95	$42.90
Purchase #5	$14.70	11.371%	$16.3715	$16.37	$16.35	$16.40
Purchase #6	$30.32	9.611%	$33.2341	$33.23	$33.25	$33.20
Purchase #7	$39.67	12.553%	$44.6498	$44.65	$44.65	$44.60
7 purchase totals =	$462.96		$500.7775	$500.77	$500.75	$500.80