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	$90.48	12.189%	$101.5086	$101.51	$101.50	$101.50
Purchase #2	$128.83	10.356%	$142.1716	$142.17	$142.15	$142.20
Purchase #3	$81.45	5.845%	$86.2108	$86.21	$86.20	$86.20
Purchase #4	$34.28	10.363%	$37.8324	$37.83	$37.85	$37.80
Purchase #5	$151.98	10.873%	$168.5048	$168.50	$168.50	$168.50
Purchase #6	$197.25	12.272%	$221.4565	$221.46	$221.45	$221.50
Purchase #7	$22.70	9.248%	$24.7993	$24.80	$24.80	$24.80
7 purchase totals =	$706.97		$782.4840	$782.48	$782.45	$782.50