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	$128.52	7.480%	$138.1333	$138.13	$138.15	$138.10
Purchase #2	$213.84	13.114%	$241.883	$241.88	$241.90	$241.90
Purchase #3	$109.93	12.726%	$123.9197	$123.92	$123.90	$123.90
Purchase #4	$110.26	6.684%	$117.6298	$117.63	$117.65	$117.60
Purchase #5	$247.60	8.428%	$268.4677	$268.47	$268.45	$268.50
Purchase #6	$42.85	12.140%	$48.052	$48.05	$48.05	$48.10
Purchase #7	$117.55	5.338%	$123.8248	$123.82	$123.80	$123.80
7 purchase totals =	$970.55		$1,061.9103	$1,061.90	$1,061.90	$1,061.90