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	$6.44	7.690%	$6.9352	$6.94	$6.95	$6.90
Purchase #2	$105.56	5.605%	$111.4766	$111.48	$111.50	$111.50
Purchase #3	$204.47	5.569%	$215.8569	$215.86	$215.85	$215.90
Purchase #4	$55.33	12.604%	$62.3038	$62.30	$62.30	$62.30
Purchase #5	$243.62	8.660%	$264.7175	$264.72	$264.70	$264.70
Purchase #6	$174.38	4.851%	$182.8392	$182.84	$182.85	$182.80
Purchase #7	$40.94	12.196%	$45.933	$45.93	$45.95	$45.90
7 purchase totals =	$830.74		$890.0622	$890.07	$890.10	$890.00