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	$46.84	12.437%	$52.6655	$52.67	$52.65	$52.70
Purchase #2	$198.62	4.189%	$206.9402	$206.94	$206.95	$206.90
Purchase #3	$85.26	6.548%	$90.8428	$90.84	$90.85	$90.80
Purchase #4	$103.79	6.834%	$110.883	$110.88	$110.90	$110.90
Purchase #5	$188.54	13.457%	$213.9118	$213.91	$213.90	$213.90
Purchase #6	$36.80	8.416%	$39.8971	$39.90	$39.90	$39.90
Purchase #7	$115.37	7.395%	$123.9016	$123.90	$123.90	$123.90
7 purchase totals =	$775.22		$839.0420	$839.04	$839.05	$839.00