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	$81.25	12.470%	$91.3819	$91.38	$91.40	$91.40
Purchase #2	$188.45	6.422%	$200.5523	$200.55	$200.55	$200.60
Purchase #3	$85.69	13.809%	$97.5229	$97.52	$97.50	$97.50
Purchase #4	$157.79	9.187%	$172.2862	$172.29	$172.30	$172.30
Purchase #5	$21.47	9.435%	$23.4957	$23.50	$23.50	$23.50
Purchase #6	$113.51	5.617%	$119.8859	$119.89	$119.90	$119.90
Purchase #7	$243.96	10.241%	$268.9439	$268.94	$268.95	$268.90
7 purchase totals =	$892.12		$974.0688	$974.07	$974.10	$974.10