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	$46.27	11.604%	$51.6392	$51.64	$51.65	$51.60
Purchase #2	$176.48	3.642%	$182.9074	$182.91	$182.90	$182.90
Purchase #3	$28.57	13.843%	$32.5249	$32.52	$32.50	$32.50
Purchase #4	$80.55	12.413%	$90.5487	$90.55	$90.55	$90.50
Purchase #5	$235.80	12.467%	$265.1972	$265.20	$265.20	$265.20
Purchase #6	$186.98	13.859%	$212.8936	$212.89	$212.90	$212.90
Purchase #7	$38.28	9.189%	$41.7975	$41.80	$41.80	$41.80
7 purchase totals =	$792.93		$877.5085	$877.51	$877.50	$877.40