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	$84.42	5.466%	$89.0344	$89.03	$89.05	$89.00
Purchase #2	$144.85	11.462%	$161.4527	$161.45	$161.45	$161.50
Purchase #3	$42.77	10.137%	$47.1056	$47.11	$47.10	$47.10
Purchase #4	$7.50	5.184%	$7.8888	$7.89	$7.90	$7.90
Purchase #5	$171.58	13.114%	$194.081	$194.08	$194.10	$194.10
Purchase #6	$76.36	13.793%	$86.8923	$86.89	$86.90	$86.90
Purchase #7	$111.44	5.438%	$117.5001	$117.50	$117.50	$117.50
7 purchase totals =	$638.92		$703.9549	$703.95	$704.00	$704.00