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	$126.49	12.447%	$142.2342	$142.23	$142.25	$142.20
Purchase #2	$49.41	4.614%	$51.6898	$51.69	$51.70	$51.70
Purchase #3	$137.64	9.593%	$150.8438	$150.84	$150.85	$150.80
Purchase #4	$109.29	7.554%	$117.5458	$117.55	$117.55	$117.50
Purchase #5	$97.50	3.389%	$100.8043	$100.80	$100.80	$100.80
Purchase #6	$174.79	5.484%	$184.3755	$184.38	$184.40	$184.40
Purchase #7	$242.50	11.334%	$269.985	$269.99	$270.00	$270.00
7 purchase totals =	$937.62		$1,017.4784	$1,017.48	$1,017.55	$1,017.40