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	$83.95	8.227%	$90.8566	$90.86	$90.85	$90.90
Purchase #2	$81.76	10.357%	$90.2279	$90.23	$90.25	$90.20
Purchase #3	$78.33	6.273%	$83.2436	$83.24	$83.25	$83.20
Purchase #4	$211.93	5.534%	$223.6582	$223.66	$223.65	$223.70
Purchase #5	$26.45	3.659%	$27.4178	$27.42	$27.40	$27.40
Purchase #6	$121.34	6.200%	$128.8631	$128.86	$128.85	$128.90
Purchase #7	$163.72	9.156%	$178.7102	$178.71	$178.70	$178.70
7 purchase totals =	$767.48		$822.9774	$822.98	$822.95	$823.00