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	$91.45	12.870%	$103.2196	$103.22	$103.20	$103.20
Purchase #2	$164.54	11.573%	$183.5822	$183.58	$183.60	$183.60
Purchase #3	$151.47	8.535%	$164.398	$164.40	$164.40	$164.40
Purchase #4	$6.39	6.332%	$6.7946	$6.79	$6.80	$6.80
Purchase #5	$47.75	3.614%	$49.4757	$49.48	$49.50	$49.50
Purchase #6	$72.90	13.232%	$82.5461	$82.55	$82.55	$82.50
Purchase #7	$92.42	4.827%	$96.8811	$96.88	$96.90	$96.90
7 purchase totals =	$626.92		$686.8973	$686.90	$686.95	$686.90