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	$63.45	9.803%	$69.67	$69.67	$69.65	$69.70
Purchase #2	$220.41	5.171%	$231.8074	$231.81	$231.80	$231.80
Purchase #3	$25.41	6.746%	$27.1242	$27.12	$27.10	$27.10
Purchase #4	$165.56	10.617%	$183.1375	$183.14	$183.15	$183.10
Purchase #5	$156.66	5.599%	$165.4314	$165.43	$165.45	$165.40
Purchase #6	$59.76	13.676%	$67.9328	$67.93	$67.95	$67.90
Purchase #7	$139.64	3.756%	$144.8849	$144.88	$144.90	$144.90
7 purchase totals =	$830.89		$889.9882	$889.98	$890.00	$889.90