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	$80.66	3.105%	$83.1645	$83.16	$83.15	$83.20
Purchase #2	$87.45	4.527%	$91.4089	$91.41	$91.40	$91.40
Purchase #3	$205.72	6.524%	$219.1412	$219.14	$219.15	$219.10
Purchase #4	$81.68	10.829%	$90.5251	$90.53	$90.55	$90.50
Purchase #5	$195.96	13.800%	$223.0025	$223.00	$223.00	$223.00
Purchase #6	$45.30	3.436%	$46.8565	$46.86	$46.85	$46.90
Purchase #7	$6.40	8.110%	$6.919	$6.92	$6.90	$6.90
7 purchase totals =	$703.17		$761.0177	$761.02	$761.00	$761.00