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	$114.98	11.769%	$128.512	$128.51	$128.50	$128.50
Purchase #2	$199.68	6.779%	$213.2163	$213.22	$213.20	$213.20
Purchase #3	$119.29	9.709%	$130.8719	$130.87	$130.85	$130.90
Purchase #4	$43.75	3.244%	$45.1693	$45.17	$45.15	$45.20
Purchase #5	$117.74	11.682%	$131.4944	$131.49	$131.50	$131.50
Purchase #6	$163.92	4.342%	$171.0374	$171.04	$171.05	$171.00
Purchase #7	$29.45	7.629%	$31.6967	$31.70	$31.70	$31.70
7 purchase totals =	$788.81		$851.9980	$852.00	$851.95	$852.00