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	$109.89	5.179%	$115.5812	$115.58	$115.60	$115.60
Purchase #2	$95.91	4.696%	$100.4139	$100.41	$100.40	$100.40
Purchase #3	$75.33	13.463%	$85.4717	$85.47	$85.45	$85.50
Purchase #4	$41.76	12.190%	$46.8505	$46.85	$46.85	$46.90
Purchase #5	$82.92	3.675%	$85.9673	$85.97	$85.95	$86.00
Purchase #6	$163.33	13.380%	$185.1836	$185.18	$185.20	$185.20
Purchase #7	$136.27	5.480%	$143.7376	$143.74	$143.75	$143.70
7 purchase totals =	$705.41		$763.2058	$763.20	$763.20	$763.30