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	$136.59	4.358%	$142.5426	$142.54	$142.55	$142.50
Purchase #2	$165.38	8.280%	$179.0735	$179.07	$179.05	$179.10
Purchase #3	$23.96	6.382%	$25.4891	$25.49	$25.50	$25.50
Purchase #4	$234.60	10.386%	$258.9656	$258.97	$258.95	$259.00
Purchase #5	$36.43	13.855%	$41.4774	$41.48	$41.50	$41.50
Purchase #6	$83.32	13.821%	$94.8357	$94.84	$94.85	$94.80
Purchase #7	$11.51	11.727%	$12.8598	$12.86	$12.85	$12.90
7 purchase totals =	$691.79		$755.2437	$755.25	$755.25	$755.30