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	$6.50	11.854%	$7.2705	$7.27	$7.25	$7.30
Purchase #2	$163.45	6.542%	$174.1429	$174.14	$174.15	$174.10
Purchase #3	$43.57	12.760%	$49.1295	$49.13	$49.15	$49.10
Purchase #4	$74.37	12.304%	$83.5205	$83.52	$83.50	$83.50
Purchase #5	$13.55	12.162%	$15.198	$15.20	$15.20	$15.20
Purchase #6	$128.56	8.531%	$139.5275	$139.53	$139.55	$139.50
Purchase #7	$54.30	8.709%	$59.029	$59.03	$59.05	$59.00
7 purchase totals =	$484.30		$527.8179	$527.82	$527.85	$527.70