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	$80.36	7.538%	$86.4175	$86.42	$86.40	$86.40
Purchase #2	$65.61	9.844%	$72.0686	$72.07	$72.05	$72.10
Purchase #3	$100.56	11.461%	$112.0852	$112.09	$112.10	$112.10
Purchase #4	$138.85	12.588%	$156.3284	$156.33	$156.35	$156.30
Purchase #5	$55.33	5.340%	$58.2846	$58.28	$58.30	$58.30
Purchase #6	$248.93	6.667%	$265.5262	$265.53	$265.55	$265.50
Purchase #7	$122.26	13.833%	$139.1722	$139.17	$139.15	$139.20
7 purchase totals =	$811.90		$889.8827	$889.89	$889.90	$889.90