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	$86.46	9.288%	$94.4904	$94.49	$94.50	$94.50
Purchase #2	$135.88	10.678%	$150.3893	$150.39	$150.40	$150.40
Purchase #3	$16.94	8.787%	$18.4285	$18.43	$18.45	$18.40
Purchase #4	$69.78	12.770%	$78.6909	$78.69	$78.70	$78.70
Purchase #5	$27.77	11.674%	$31.0119	$31.01	$31.00	$31.00
Purchase #6	$105.76	3.369%	$109.3231	$109.32	$109.30	$109.30
Purchase #7	$148.72	5.820%	$157.3755	$157.38	$157.40	$157.40
7 purchase totals =	$591.31		$639.7096	$639.71	$639.75	$639.70