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	$221.42	4.531%	$231.4525	$231.45	$231.45	$231.50
Purchase #2	$70.72	13.248%	$80.089	$80.09	$80.10	$80.10
Purchase #3	$202.35	5.415%	$213.3073	$213.31	$213.30	$213.30
Purchase #4	$145.44	3.462%	$150.4751	$150.48	$150.50	$150.50
Purchase #5	$127.77	10.369%	$141.0185	$141.02	$141.00	$141.00
Purchase #6	$246.31	3.747%	$255.5392	$255.54	$255.55	$255.50
Purchase #7	$219.63	10.156%	$241.9356	$241.94	$241.95	$241.90
7 purchase totals =	$1,233.64		$1,313.8172	$1,313.83	$1,313.85	$1,313.80