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	$8.92	10.748%	$9.8787	$9.88	$9.90	$9.90
Purchase #2	$66.78	8.523%	$72.4717	$72.47	$72.45	$72.50
Purchase #3	$191.30	11.127%	$212.586	$212.59	$212.60	$212.60
Purchase #4	$161.98	4.860%	$169.8522	$169.85	$169.85	$169.90
Purchase #5	$97.89	3.428%	$101.2457	$101.25	$101.25	$101.20
Purchase #6	$28.86	13.592%	$32.7827	$32.78	$32.80	$32.80
Purchase #7	$233.57	6.398%	$248.5138	$248.51	$248.50	$248.50
7 purchase totals =	$789.30		$847.3308	$847.33	$847.35	$847.40