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	$133.85	4.639%	$140.0593	$140.06	$140.05	$140.10
Purchase #2	$175.88	7.129%	$188.4185	$188.42	$188.40	$188.40
Purchase #3	$122.98	13.638%	$139.752	$139.75	$139.75	$139.80
Purchase #4	$137.41	5.838%	$145.432	$145.43	$145.45	$145.40
Purchase #5	$97.33	8.154%	$105.2663	$105.27	$105.25	$105.30
Purchase #6	$33.92	11.606%	$37.8568	$37.86	$37.85	$37.90
Purchase #7	$229.56	13.600%	$260.7802	$260.78	$260.80	$260.80
7 purchase totals =	$930.93		$1,017.5651	$1,017.57	$1,017.55	$1,017.70