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	$25.55	11.437%	$28.4722	$28.47	$28.45	$28.50
Purchase #2	$198.89	11.831%	$222.4207	$222.42	$222.40	$222.40
Purchase #3	$162.84	12.602%	$183.3611	$183.36	$183.35	$183.40
Purchase #4	$113.98	5.798%	$120.5886	$120.59	$120.60	$120.60
Purchase #5	$192.72	3.754%	$199.9547	$199.95	$199.95	$200.00
Purchase #6	$59.94	8.174%	$64.8395	$64.84	$64.85	$64.80
Purchase #7	$73.89	5.767%	$78.1512	$78.15	$78.15	$78.20
7 purchase totals =	$827.81		$897.7880	$897.78	$897.75	$897.90