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	$32.59	10.199%	$35.9139	$35.91	$35.90	$35.90
Purchase #2	$145.50	7.531%	$156.4576	$156.46	$156.45	$156.50
Purchase #3	$73.98	7.669%	$79.6535	$79.65	$79.65	$79.70
Purchase #4	$63.71	13.505%	$72.314	$72.31	$72.30	$72.30
Purchase #5	$205.86	4.103%	$214.3064	$214.31	$214.30	$214.30
Purchase #6	$115.47	10.550%	$127.6521	$127.65	$127.65	$127.70
Purchase #7	$189.73	12.615%	$213.6644	$213.66	$213.65	$213.70
7 purchase totals =	$826.84		$899.9619	$899.95	$899.90	$900.10