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	$159.67	12.566%	$179.7341	$179.73	$179.75	$179.70
Purchase #2	$21.68	11.381%	$24.1474	$24.15	$24.15	$24.10
Purchase #3	$180.91	5.320%	$190.5344	$190.53	$190.55	$190.50
Purchase #4	$191.49	12.691%	$215.792	$215.79	$215.80	$215.80
Purchase #5	$123.82	5.856%	$131.0709	$131.07	$131.05	$131.10
Purchase #6	$143.35	6.187%	$152.2191	$152.22	$152.20	$152.20
Purchase #7	$91.86	6.570%	$97.8952	$97.90	$97.90	$97.90
7 purchase totals =	$912.78		$991.3931	$991.39	$991.40	$991.30