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	$188.33	8.571%	$204.4718	$204.47	$204.45	$204.50
Purchase #2	$117.82	13.346%	$133.5443	$133.54	$133.55	$133.50
Purchase #3	$150.95	5.250%	$158.8749	$158.87	$158.85	$158.90
Purchase #4	$135.32	5.474%	$142.7274	$142.73	$142.75	$142.70
Purchase #5	$80.34	12.599%	$90.462	$90.46	$90.45	$90.50
Purchase #6	$101.75	10.109%	$112.0359	$112.04	$112.05	$112.00
Purchase #7	$63.31	13.460%	$71.8315	$71.83	$71.85	$71.80
7 purchase totals =	$837.82		$913.9478	$913.94	$913.95	$913.90