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	$42.36	12.352%	$47.5923	$47.59	$47.60	$47.60
Purchase #2	$223.59	12.213%	$250.897	$250.90	$250.90	$250.90
Purchase #3	$155.32	9.182%	$169.5815	$169.58	$169.60	$169.60
Purchase #4	$242.55	8.196%	$262.4294	$262.43	$262.45	$262.40
Purchase #5	$114.25	12.411%	$128.4296	$128.43	$128.45	$128.40
Purchase #6	$127.66	8.644%	$138.6949	$138.69	$138.70	$138.70
Purchase #7	$74.96	10.667%	$82.956	$82.96	$82.95	$83.00
7 purchase totals =	$980.69		$1,080.5807	$1,080.58	$1,080.65	$1,080.60