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	$128.80	6.528%	$137.2081	$137.21	$137.20	$137.20
Purchase #2	$219.44	12.763%	$247.4471	$247.45	$247.45	$247.40
Purchase #3	$176.84	4.339%	$184.5131	$184.51	$184.50	$184.50
Purchase #4	$75.97	13.172%	$85.9768	$85.98	$86.00	$86.00
Purchase #5	$163.59	13.445%	$185.5847	$185.58	$185.60	$185.60
Purchase #6	$92.52	6.269%	$98.3201	$98.32	$98.30	$98.30
Purchase #7	$69.50	4.120%	$72.3634	$72.36	$72.35	$72.40
7 purchase totals =	$926.66		$1,011.4133	$1,011.41	$1,011.40	$1,011.40