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	$104.65	6.524%	$111.4774	$111.48	$111.50	$111.50
Purchase #2	$183.83	8.243%	$198.9831	$198.98	$199.00	$199.00
Purchase #3	$161.31	7.140%	$172.8275	$172.83	$172.85	$172.80
Purchase #4	$151.41	8.829%	$164.778	$164.78	$164.80	$164.80
Purchase #5	$42.46	13.558%	$48.2167	$48.22	$48.20	$48.20
Purchase #6	$71.31	9.499%	$78.0837	$78.08	$78.10	$78.10
Purchase #7	$84.96	3.571%	$87.9939	$87.99	$88.00	$88.00
7 purchase totals =	$799.93		$862.3603	$862.36	$862.45	$862.40