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	$38.62	13.649%	$43.8912	$43.89	$43.90	$43.90
Purchase #2	$81.75	12.262%	$91.7742	$91.77	$91.75	$91.80
Purchase #3	$203.29	3.275%	$209.9477	$209.95	$209.95	$209.90
Purchase #4	$135.43	12.861%	$152.8477	$152.85	$152.85	$152.80
Purchase #5	$141.83	5.462%	$149.5768	$149.58	$149.60	$149.60
Purchase #6	$76.51	13.574%	$86.8955	$86.90	$86.90	$86.90
Purchase #7	$56.52	12.339%	$63.494	$63.49	$63.50	$63.50
7 purchase totals =	$733.95		$798.4271	$798.43	$798.45	$798.40