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	$108.49	3.843%	$112.6593	$112.66	$112.65	$112.70
Purchase #2	$13.36	10.612%	$14.7778	$14.78	$14.80	$14.80
Purchase #3	$100.40	5.210%	$105.6308	$105.63	$105.65	$105.60
Purchase #4	$124.84	5.618%	$131.8535	$131.85	$131.85	$131.90
Purchase #5	$160.29	4.742%	$167.891	$167.89	$167.90	$167.90
Purchase #6	$140.67	7.580%	$151.3328	$151.33	$151.35	$151.30
Purchase #7	$144.27	8.488%	$156.5156	$156.52	$156.50	$156.50
7 purchase totals =	$792.32		$840.6608	$840.66	$840.70	$840.70