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	$15.61	12.361%	$17.5396	$17.54	$17.55	$17.50
Purchase #2	$144.46	11.395%	$160.9212	$160.92	$160.90	$160.90
Purchase #3	$107.37	4.627%	$112.338	$112.34	$112.35	$112.30
Purchase #4	$180.25	5.687%	$190.5008	$190.50	$190.50	$190.50
Purchase #5	$9.71	11.669%	$10.8431	$10.84	$10.85	$10.80
Purchase #6	$157.35	9.182%	$171.7979	$171.80	$171.80	$171.80
Purchase #7	$85.25	5.255%	$89.7299	$89.73	$89.75	$89.70
7 purchase totals =	$700.00		$753.6705	$753.67	$753.70	$753.50