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	$36.92	13.145%	$41.7731	$41.77	$41.75	$41.80
Purchase #2	$98.88	10.238%	$109.0033	$109.00	$109.00	$109.00
Purchase #3	$28.77	8.205%	$31.1306	$31.13	$31.15	$31.10
Purchase #4	$196.44	3.758%	$203.8222	$203.82	$203.80	$203.80
Purchase #5	$165.81	5.303%	$174.6029	$174.60	$174.60	$174.60
Purchase #6	$62.30	6.545%	$66.3775	$66.38	$66.40	$66.40
Purchase #7	$55.98	9.258%	$61.1626	$61.16	$61.15	$61.20
7 purchase totals =	$645.10		$687.8722	$687.86	$687.85	$687.90