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	$218.91	5.732%	$231.4579	$231.46	$231.45	$231.50
Purchase #2	$134.31	10.407%	$148.2876	$148.29	$148.30	$148.30
Purchase #3	$178.38	7.442%	$191.655	$191.66	$191.65	$191.70
Purchase #4	$126.81	8.467%	$137.547	$137.55	$137.55	$137.50
Purchase #5	$145.38	3.857%	$150.9873	$150.99	$151.00	$151.00
Purchase #6	$27.36	5.242%	$28.7942	$28.79	$28.80	$28.80
Purchase #7	$151.55	11.179%	$168.4918	$168.49	$168.50	$168.50
7 purchase totals =	$982.70		$1,057.2208	$1,057.23	$1,057.25	$1,057.30