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	$18.95	5.626%	$20.0161	$20.02	$20.00	$20.00
Purchase #2	$18.62	7.492%	$20.015	$20.02	$20.00	$20.00
Purchase #3	$22.54	9.350%	$24.6475	$24.65	$24.65	$24.60
Purchase #4	$33.94	4.458%	$35.453	$35.45	$35.45	$35.50
Purchase #5	$213.60	4.112%	$222.3832	$222.38	$222.40	$222.40
Purchase #6	$49.88	10.139%	$54.9373	$54.94	$54.95	$54.90
Purchase #7	$142.31	13.322%	$161.2685	$161.27	$161.25	$161.30
7 purchase totals =	$499.84		$538.7206	$538.73	$538.70	$538.70