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	$28.35	12.207%	$31.8107	$31.81	$31.80	$31.80
Purchase #2	$226.54	5.558%	$239.1311	$239.13	$239.15	$239.10
Purchase #3	$172.96	10.201%	$190.6036	$190.60	$190.60	$190.60
Purchase #4	$114.37	12.320%	$128.4604	$128.46	$128.45	$128.50
Purchase #5	$176.67	6.682%	$188.4751	$188.48	$188.50	$188.50
Purchase #6	$226.34	7.198%	$242.632	$242.63	$242.65	$242.60
Purchase #7	$155.31	10.835%	$172.1378	$172.14	$172.15	$172.10
7 purchase totals =	$1,100.54		$1,193.2507	$1,193.25	$1,193.30	$1,193.20