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	$121.87	5.329%	$128.3645	$128.36	$128.35	$128.40
Purchase #2	$138.40	8.759%	$150.5225	$150.52	$150.50	$150.50
Purchase #3	$222.67	10.427%	$245.8878	$245.89	$245.90	$245.90
Purchase #4	$127.56	5.425%	$134.4801	$134.48	$134.50	$134.50
Purchase #5	$57.89	3.525%	$59.9306	$59.93	$59.95	$59.90
Purchase #6	$127.32	13.653%	$144.703	$144.70	$144.70	$144.70
Purchase #7	$214.96	9.840%	$236.1121	$236.11	$236.10	$236.10
7 purchase totals =	$1,010.67		$1,100.0006	$1,099.99	$1,100.00	$1,100.00