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	$128.96	9.404%	$141.0874	$141.09	$141.10	$141.10
Purchase #2	$144.26	5.758%	$152.5665	$152.57	$152.55	$152.60
Purchase #3	$164.33	5.350%	$173.1217	$173.12	$173.10	$173.10
Purchase #4	$50.96	6.437%	$54.2403	$54.24	$54.25	$54.20
Purchase #5	$100.48	13.189%	$113.7323	$113.73	$113.75	$113.70
Purchase #6	$151.74	7.323%	$162.8519	$162.85	$162.85	$162.90
Purchase #7	$115.90	6.600%	$123.5494	$123.55	$123.55	$123.50
7 purchase totals =	$856.63		$921.1495	$921.15	$921.15	$921.10