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	$22.60	9.518%	$24.7511	$24.75	$24.75	$24.80
Purchase #2	$26.53	10.477%	$29.3095	$29.31	$29.30	$29.30
Purchase #3	$82.91	13.654%	$94.2305	$94.23	$94.25	$94.20
Purchase #4	$132.69	6.694%	$141.5723	$141.57	$141.55	$141.60
Purchase #5	$131.32	7.258%	$140.8512	$140.85	$140.85	$140.90
Purchase #6	$184.30	6.484%	$196.25	$196.25	$196.25	$196.30
Purchase #7	$159.25	3.270%	$164.4575	$164.46	$164.45	$164.50
7 purchase totals =	$739.60		$791.4221	$791.42	$791.40	$791.60