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	$121.66	5.592%	$128.4632	$128.46	$128.45	$128.50
Purchase #2	$245.71	10.341%	$271.1189	$271.12	$271.10	$271.10
Purchase #3	$137.41	12.508%	$154.5972	$154.60	$154.60	$154.60
Purchase #4	$174.75	3.862%	$181.4988	$181.50	$181.50	$181.50
Purchase #5	$242.95	8.180%	$262.8233	$262.82	$262.80	$262.80
Purchase #6	$172.72	4.728%	$180.8862	$180.89	$180.90	$180.90
Purchase #7	$210.83	4.429%	$220.1677	$220.17	$220.15	$220.20
7 purchase totals =	$1,306.03		$1,399.5553	$1,399.56	$1,399.50	$1,399.60