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	$52.95	4.874%	$55.5308	$55.53	$55.55	$55.50
Purchase #2	$150.75	9.114%	$164.4894	$164.49	$164.50	$164.50
Purchase #3	$83.37	8.588%	$90.5298	$90.53	$90.55	$90.50
Purchase #4	$29.85	4.492%	$31.1909	$31.19	$31.20	$31.20
Purchase #5	$21.45	4.318%	$22.3762	$22.38	$22.40	$22.40
Purchase #6	$197.30	7.838%	$212.7644	$212.76	$212.75	$212.80
Purchase #7	$55.34	11.203%	$61.5397	$61.54	$61.55	$61.50
7 purchase totals =	$591.01		$638.4212	$638.42	$638.50	$638.40