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	$91.58	9.689%	$100.4532	$100.45	$100.45	$100.50
Purchase #2	$116.32	12.636%	$131.0182	$131.02	$131.00	$131.00
Purchase #3	$38.83	9.593%	$42.555	$42.56	$42.55	$42.60
Purchase #4	$65.48	10.850%	$72.5846	$72.58	$72.60	$72.60
Purchase #5	$187.60	7.736%	$202.1127	$202.11	$202.10	$202.10
Purchase #6	$80.73	4.644%	$84.4791	$84.48	$84.50	$84.50
Purchase #7	$129.58	5.870%	$137.1863	$137.19	$137.20	$137.20
7 purchase totals =	$710.12		$770.3891	$770.39	$770.40	$770.50