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	$123.54	10.495%	$136.5055	$136.51	$136.50	$136.50
Purchase #2	$214.98	7.638%	$231.4002	$231.40	$231.40	$231.40
Purchase #3	$89.85	12.243%	$100.8503	$100.85	$100.85	$100.90
Purchase #4	$249.33	7.332%	$267.6109	$267.61	$267.60	$267.60
Purchase #5	$171.61	11.409%	$191.189	$191.19	$191.20	$191.20
Purchase #6	$31.84	4.322%	$33.2161	$33.22	$33.20	$33.20
Purchase #7	$89.73	8.684%	$97.5222	$97.52	$97.50	$97.50
7 purchase totals =	$970.88		$1,058.2942	$1,058.30	$1,058.25	$1,058.30