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	$234.85	6.158%	$249.3121	$249.31	$249.30	$249.30
Purchase #2	$248.97	13.582%	$282.7851	$282.79	$282.80	$282.80
Purchase #3	$135.53	5.448%	$142.9137	$142.91	$142.90	$142.90
Purchase #4	$211.87	10.855%	$234.8685	$234.87	$234.85	$234.90
Purchase #5	$226.83	6.320%	$241.1657	$241.17	$241.15	$241.20
Purchase #6	$38.55	4.223%	$40.178	$40.18	$40.20	$40.20
Purchase #7	$178.89	3.766%	$185.627	$185.63	$185.65	$185.60
7 purchase totals =	$1,275.49		$1,376.8501	$1,376.86	$1,376.85	$1,376.90