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	$63.54	6.609%	$67.7394	$67.74	$67.75	$67.70
Purchase #2	$171.93	6.196%	$182.5828	$182.58	$182.60	$182.60
Purchase #3	$120.63	5.104%	$126.787	$126.79	$126.80	$126.80
Purchase #4	$38.25	9.458%	$41.8677	$41.87	$41.85	$41.90
Purchase #5	$41.28	4.460%	$43.1211	$43.12	$43.10	$43.10
Purchase #6	$88.55	13.363%	$100.3829	$100.38	$100.40	$100.40
Purchase #7	$249.52	7.800%	$268.9826	$268.98	$269.00	$269.00
7 purchase totals =	$773.70		$831.4635	$831.46	$831.50	$831.50