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	$31.32	6.812%	$33.4535	$33.45	$33.45	$33.50
Purchase #2	$163.88	4.637%	$171.4791	$171.48	$171.50	$171.50
Purchase #3	$245.98	13.220%	$278.4986	$278.50	$278.50	$278.50
Purchase #4	$98.45	4.166%	$102.5514	$102.55	$102.55	$102.60
Purchase #5	$159.39	8.406%	$172.7883	$172.79	$172.80	$172.80
Purchase #6	$74.56	9.376%	$81.5507	$81.55	$81.55	$81.60
Purchase #7	$133.87	12.242%	$150.2584	$150.26	$150.25	$150.30
7 purchase totals =	$907.45		$990.5800	$990.58	$990.60	$990.80