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	$29.50	7.854%	$31.8169	$31.82	$31.80	$31.80
Purchase #2	$102.44	9.269%	$111.9352	$111.94	$111.95	$111.90
Purchase #3	$158.56	11.328%	$176.5217	$176.52	$176.50	$176.50
Purchase #4	$158.51	5.693%	$167.534	$167.53	$167.55	$167.50
Purchase #5	$86.25	11.670%	$96.3154	$96.32	$96.30	$96.30
Purchase #6	$188.85	9.465%	$206.7247	$206.72	$206.70	$206.70
Purchase #7	$90.94	6.530%	$96.8784	$96.88	$96.90	$96.90
7 purchase totals =	$815.05		$887.7263	$887.73	$887.70	$887.60