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	$27.49	13.661%	$31.2454	$31.25	$31.25	$31.20
Purchase #2	$152.58	5.261%	$160.6072	$160.61	$160.60	$160.60
Purchase #3	$234.89	10.247%	$258.9592	$258.96	$258.95	$259.00
Purchase #4	$139.68	5.872%	$147.882	$147.88	$147.90	$147.90
Purchase #5	$229.97	10.403%	$253.8938	$253.89	$253.90	$253.90
Purchase #6	$227.36	5.626%	$240.1513	$240.15	$240.15	$240.20
Purchase #7	$128.46	9.624%	$140.823	$140.82	$140.80	$140.80
7 purchase totals =	$1,140.43		$1,233.5619	$1,233.56	$1,233.55	$1,233.60