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	$34.83	11.280%	$38.7588	$38.76	$38.75	$38.80
Purchase #2	$120.88	4.815%	$126.7004	$126.70	$126.70	$126.70
Purchase #3	$102.72	11.171%	$114.1949	$114.19	$114.20	$114.20
Purchase #4	$166.39	9.156%	$181.6247	$181.62	$181.60	$181.60
Purchase #5	$71.44	9.474%	$78.2082	$78.21	$78.20	$78.20
Purchase #6	$18.72	11.780%	$20.9252	$20.93	$20.95	$20.90
Purchase #7	$98.95	8.124%	$106.9887	$106.99	$107.00	$107.00
7 purchase totals =	$613.93		$667.4009	$667.40	$667.40	$667.40