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	$26.97	3.663%	$27.9579	$27.96	$27.95	$28.00
Purchase #2	$154.62	6.404%	$164.5219	$164.52	$164.50	$164.50
Purchase #3	$162.64	9.318%	$177.7948	$177.79	$177.80	$177.80
Purchase #4	$30.37	8.268%	$32.881	$32.88	$32.90	$32.90
Purchase #5	$162.42	4.353%	$169.4901	$169.49	$169.50	$169.50
Purchase #6	$86.48	3.791%	$89.7585	$89.76	$89.75	$89.80
Purchase #7	$243.54	9.434%	$266.5156	$266.52	$266.50	$266.50
7 purchase totals =	$867.04		$928.9198	$928.92	$928.90	$929.00