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	$137.76	7.136%	$147.5906	$147.59	$147.60	$147.60
Purchase #2	$36.72	7.386%	$39.4321	$39.43	$39.45	$39.40
Purchase #3	$106.30	12.352%	$119.4302	$119.43	$119.45	$119.40
Purchase #4	$86.66	11.398%	$96.5375	$96.54	$96.55	$96.50
Purchase #5	$83.60	8.517%	$90.7202	$90.72	$90.70	$90.70
Purchase #6	$104.99	6.658%	$111.9802	$111.98	$112.00	$112.00
Purchase #7	$194.86	4.677%	$203.9736	$203.97	$203.95	$204.00
7 purchase totals =	$750.89		$809.6644	$809.66	$809.70	$809.60