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	$206.51	10.266%	$227.7103	$227.71	$227.70	$227.70
Purchase #2	$97.42	8.140%	$105.35	$105.35	$105.35	$105.40
Purchase #3	$91.25	8.191%	$98.7243	$98.72	$98.70	$98.70
Purchase #4	$18.61	12.624%	$20.9593	$20.96	$20.95	$21.00
Purchase #5	$168.34	13.178%	$190.5238	$190.52	$190.50	$190.50
Purchase #6	$54.61	8.451%	$59.2251	$59.23	$59.25	$59.20
Purchase #7	$183.77	10.430%	$202.9372	$202.94	$202.95	$202.90
7 purchase totals =	$820.51		$905.4300	$905.43	$905.40	$905.40