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	$80.29	3.369%	$82.995	$83.00	$83.00	$83.00
Purchase #2	$176.33	6.711%	$188.1635	$188.16	$188.15	$188.20
Purchase #3	$49.52	8.190%	$53.5757	$53.58	$53.60	$53.60
Purchase #4	$249.46	6.393%	$265.408	$265.41	$265.40	$265.40
Purchase #5	$92.64	8.576%	$100.5848	$100.58	$100.60	$100.60
Purchase #6	$57.88	7.814%	$62.4027	$62.40	$62.40	$62.40
Purchase #7	$95.76	10.634%	$105.9431	$105.94	$105.95	$105.90
7 purchase totals =	$801.88		$859.0728	$859.07	$859.10	$859.10