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	$249.69	10.365%	$275.5704	$275.57	$275.55	$275.60
Purchase #2	$116.72	5.581%	$123.2341	$123.23	$123.25	$123.20
Purchase #3	$51.80	7.515%	$55.6928	$55.69	$55.70	$55.70
Purchase #4	$144.52	4.223%	$150.6231	$150.62	$150.60	$150.60
Purchase #5	$118.49	6.839%	$126.5935	$126.59	$126.60	$126.60
Purchase #6	$117.44	5.611%	$124.0296	$124.03	$124.05	$124.00
Purchase #7	$39.50	3.442%	$40.8596	$40.86	$40.85	$40.90
7 purchase totals =	$838.16		$896.6031	$896.59	$896.60	$896.60