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	$209.83	3.659%	$217.5077	$217.51	$217.50	$217.50
Purchase #2	$139.43	7.789%	$150.2902	$150.29	$150.30	$150.30
Purchase #3	$112.54	7.273%	$120.725	$120.73	$120.75	$120.70
Purchase #4	$46.88	13.418%	$53.1704	$53.17	$53.15	$53.20
Purchase #5	$165.75	8.565%	$179.9465	$179.95	$179.95	$179.90
Purchase #6	$29.65	4.501%	$30.9845	$30.98	$31.00	$31.00
Purchase #7	$152.86	10.419%	$168.7865	$168.79	$168.80	$168.80
7 purchase totals =	$856.94		$921.4108	$921.42	$921.45	$921.40