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	$82.78	9.330%	$90.5034	$90.50	$90.50	$90.50
Purchase #2	$75.31	6.456%	$80.172	$80.17	$80.15	$80.20
Purchase #3	$171.66	7.372%	$184.3148	$184.31	$184.30	$184.30
Purchase #4	$221.59	10.859%	$245.6525	$245.65	$245.65	$245.70
Purchase #5	$100.38	3.222%	$103.6142	$103.61	$103.60	$103.60
Purchase #6	$131.72	9.829%	$144.6668	$144.67	$144.65	$144.70
Purchase #7	$137.88	8.541%	$149.6563	$149.66	$149.65	$149.70
7 purchase totals =	$921.32		$998.5800	$998.57	$998.50	$998.70