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	$47.78	6.415%	$50.8451	$50.85	$50.85	$50.80
Purchase #2	$56.77	4.403%	$59.2696	$59.27	$59.25	$59.30
Purchase #3	$151.71	5.324%	$159.787	$159.79	$159.80	$159.80
Purchase #4	$228.48	9.735%	$250.7225	$250.72	$250.70	$250.70
Purchase #5	$66.61	5.760%	$70.4467	$70.45	$70.45	$70.40
Purchase #6	$237.44	12.534%	$267.2007	$267.20	$267.20	$267.20
Purchase #7	$211.88	3.666%	$219.6475	$219.65	$219.65	$219.60
7 purchase totals =	$1,000.67		$1,077.9191	$1,077.93	$1,077.90	$1,077.80