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	$11.65	10.648%	$12.8905	$12.89	$12.90	$12.90
Purchase #2	$25.55	11.630%	$28.5215	$28.52	$28.50	$28.50
Purchase #3	$76.31	13.786%	$86.8301	$86.83	$86.85	$86.80
Purchase #4	$5.45	13.629%	$6.1928	$6.19	$6.20	$6.20
Purchase #5	$63.79	4.341%	$66.5591	$66.56	$66.55	$66.60
Purchase #6	$115.41	4.695%	$120.8285	$120.83	$120.85	$120.80
Purchase #7	$162.63	10.689%	$180.0135	$180.01	$180.00	$180.00
7 purchase totals =	$460.79		$501.8360	$501.83	$501.85	$501.80