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	$148.33	6.187%	$157.5072	$157.51	$157.50	$157.50
Purchase #2	$163.62	13.772%	$186.1537	$186.15	$186.15	$186.20
Purchase #3	$81.82	10.273%	$90.2254	$90.23	$90.25	$90.20
Purchase #4	$110.96	7.455%	$119.2321	$119.23	$119.25	$119.20
Purchase #5	$12.85	11.301%	$14.3022	$14.30	$14.30	$14.30
Purchase #6	$67.82	3.800%	$70.3972	$70.40	$70.40	$70.40
Purchase #7	$37.36	8.557%	$40.5569	$40.56	$40.55	$40.60
7 purchase totals =	$622.76		$678.3747	$678.38	$678.40	$678.40