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	$111.85	7.588%	$120.3372	$120.34	$120.35	$120.30
Purchase #2	$141.42	9.144%	$154.3514	$154.35	$154.35	$154.40
Purchase #3	$130.80	11.442%	$145.7661	$145.77	$145.75	$145.80
Purchase #4	$37.80	5.845%	$40.0094	$40.01	$40.00	$40.00
Purchase #5	$76.63	7.139%	$82.1006	$82.10	$82.10	$82.10
Purchase #6	$129.88	6.182%	$137.9092	$137.91	$137.90	$137.90
Purchase #7	$41.34	3.138%	$42.6372	$42.64	$42.65	$42.60
7 purchase totals =	$669.72		$723.1111	$723.12	$723.10	$723.10