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	$123.84	5.666%	$130.8568	$130.86	$130.85	$130.90
Purchase #2	$162.36	10.456%	$179.3364	$179.34	$179.35	$179.30
Purchase #3	$104.73	6.386%	$111.4181	$111.42	$111.40	$111.40
Purchase #4	$138.87	4.312%	$144.8581	$144.86	$144.85	$144.90
Purchase #5	$79.37	13.787%	$90.3127	$90.31	$90.30	$90.30
Purchase #6	$38.79	11.206%	$43.1368	$43.14	$43.15	$43.10
Purchase #7	$121.48	13.252%	$137.5785	$137.58	$137.60	$137.60
7 purchase totals =	$769.44		$837.4974	$837.51	$837.50	$837.50