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	$150.59	5.443%	$158.7866	$158.79	$158.80	$158.80
Purchase #2	$168.50	11.182%	$187.3417	$187.34	$187.35	$187.30
Purchase #3	$72.36	12.369%	$81.3102	$81.31	$81.30	$81.30
Purchase #4	$223.95	3.522%	$231.8375	$231.84	$231.85	$231.80
Purchase #5	$96.75	6.602%	$103.1374	$103.14	$103.15	$103.10
Purchase #6	$123.55	12.787%	$139.3483	$139.35	$139.35	$139.30
Purchase #7	$39.60	4.219%	$41.2707	$41.27	$41.25	$41.30
7 purchase totals =	$875.30		$943.0324	$943.04	$943.05	$942.90