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	$85.44	4.633%	$89.3984	$89.40	$89.40	$89.40
Purchase #2	$215.59	5.444%	$227.3267	$227.33	$227.35	$227.30
Purchase #3	$246.45	13.569%	$279.8908	$279.89	$279.90	$279.90
Purchase #4	$85.65	13.660%	$97.3498	$97.35	$97.35	$97.30
Purchase #5	$89.90	12.755%	$101.3667	$101.37	$101.35	$101.40
Purchase #6	$108.59	12.526%	$122.192	$122.19	$122.20	$122.20
Purchase #7	$32.78	8.582%	$35.5932	$35.59	$35.60	$35.60
7 purchase totals =	$864.40		$953.1176	$953.12	$953.15	$953.10