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	$200.88	9.320%	$219.602	$219.60	$219.60	$219.60
Purchase #2	$54.95	3.447%	$56.8441	$56.84	$56.85	$56.80
Purchase #3	$90.34	9.760%	$99.1572	$99.16	$99.15	$99.20
Purchase #4	$84.46	9.787%	$92.7261	$92.73	$92.75	$92.70
Purchase #5	$20.88	11.531%	$23.2877	$23.29	$23.30	$23.30
Purchase #6	$98.88	13.865%	$112.5897	$112.59	$112.60	$112.60
Purchase #7	$35.49	12.422%	$39.8986	$39.90	$39.90	$39.90
7 purchase totals =	$585.88		$644.1054	$644.11	$644.15	$644.10