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	$158.59	6.369%	$168.6906	$168.69	$168.70	$168.70
Purchase #2	$78.62	4.155%	$81.8867	$81.89	$81.90	$81.90
Purchase #3	$116.47	13.240%	$131.8906	$131.89	$131.90	$131.90
Purchase #4	$136.98	13.543%	$155.5312	$155.53	$155.55	$155.50
Purchase #5	$74.28	6.852%	$79.3697	$79.37	$79.35	$79.40
Purchase #6	$176.70	7.744%	$190.3836	$190.38	$190.40	$190.40
Purchase #7	$184.79	3.139%	$190.5906	$190.59	$190.60	$190.60
7 purchase totals =	$926.43		$998.3430	$998.34	$998.40	$998.40