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	$48.74	9.776%	$53.5048	$53.50	$53.50	$53.50
Purchase #2	$83.31	5.508%	$87.8987	$87.90	$87.90	$87.90
Purchase #3	$206.75	7.120%	$221.4706	$221.47	$221.45	$221.50
Purchase #4	$123.41	6.865%	$131.8821	$131.88	$131.90	$131.90
Purchase #5	$189.73	7.655%	$204.2538	$204.25	$204.25	$204.30
Purchase #6	$136.56	5.765%	$144.4327	$144.43	$144.45	$144.40
Purchase #7	$93.84	10.302%	$103.5074	$103.51	$103.50	$103.50
7 purchase totals =	$882.34		$946.9501	$946.94	$946.95	$947.00