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	$22.86	13.193%	$25.8759	$25.88	$25.90	$25.90
Purchase #2	$136.98	12.134%	$153.6012	$153.60	$153.60	$153.60
Purchase #3	$35.38	6.397%	$37.6433	$37.64	$37.65	$37.60
Purchase #4	$152.61	11.416%	$170.032	$170.03	$170.05	$170.00
Purchase #5	$52.70	3.626%	$54.6109	$54.61	$54.60	$54.60
Purchase #6	$91.52	12.681%	$103.1257	$103.13	$103.15	$103.10
Purchase #7	$65.39	12.516%	$73.5742	$73.57	$73.55	$73.60
7 purchase totals =	$557.44		$618.4632	$618.46	$618.50	$618.40