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	$90.73	9.802%	$99.6234	$99.62	$99.60	$99.60
Purchase #2	$35.57	12.703%	$40.0885	$40.09	$40.10	$40.10
Purchase #3	$133.91	6.439%	$142.5325	$142.53	$142.55	$142.50
Purchase #4	$203.93	4.641%	$213.3944	$213.39	$213.40	$213.40
Purchase #5	$236.72	6.852%	$252.9401	$252.94	$252.95	$252.90
Purchase #6	$186.88	7.456%	$200.8138	$200.81	$200.80	$200.80
Purchase #7	$113.98	10.524%	$125.9753	$125.98	$126.00	$126.00
7 purchase totals =	$1,001.72		$1,075.3680	$1,075.36	$1,075.40	$1,075.30