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	$51.45	7.715%	$55.4194	$55.42	$55.40	$55.40
Purchase #2	$74.61	10.550%	$82.4814	$82.48	$82.50	$82.50
Purchase #3	$143.26	4.718%	$150.019	$150.02	$150.00	$150.00
Purchase #4	$72.33	13.141%	$81.8349	$81.83	$81.85	$81.80
Purchase #5	$72.40	6.255%	$76.9286	$76.93	$76.95	$76.90
Purchase #6	$105.85	6.814%	$113.0626	$113.06	$113.05	$113.10
Purchase #7	$109.36	5.465%	$115.3365	$115.34	$115.35	$115.30
7 purchase totals =	$629.26		$675.0824	$675.08	$675.10	$675.00