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	$149.89	12.406%	$168.4854	$168.49	$168.50	$168.50
Purchase #2	$134.71	8.282%	$145.8667	$145.87	$145.85	$145.90
Purchase #3	$50.38	10.480%	$55.6598	$55.66	$55.65	$55.70
Purchase #4	$76.69	10.127%	$84.4564	$84.46	$84.45	$84.50
Purchase #5	$50.56	5.554%	$53.3681	$53.37	$53.35	$53.40
Purchase #6	$156.98	3.443%	$162.3848	$162.38	$162.40	$162.40
Purchase #7	$216.95	7.755%	$233.7745	$233.77	$233.75	$233.80
7 purchase totals =	$836.16		$903.9957	$904.00	$903.95	$904.20