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	$117.57	5.670%	$124.2362	$124.24	$124.25	$124.20
Purchase #2	$104.27	13.608%	$118.4591	$118.46	$118.45	$118.50
Purchase #3	$242.45	5.332%	$255.3774	$255.38	$255.40	$255.40
Purchase #4	$16.37	12.288%	$18.3815	$18.38	$18.40	$18.40
Purchase #5	$115.46	9.696%	$126.655	$126.66	$126.65	$126.70
Purchase #6	$165.35	11.475%	$184.3239	$184.32	$184.30	$184.30
Purchase #7	$63.54	12.408%	$71.424	$71.42	$71.40	$71.40
7 purchase totals =	$825.01		$898.8571	$898.86	$898.85	$898.90