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	$28.53	7.476%	$30.6629	$30.66	$30.65	$30.70
Purchase #2	$128.85	11.307%	$143.4191	$143.42	$143.40	$143.40
Purchase #3	$113.76	12.275%	$127.724	$127.72	$127.70	$127.70
Purchase #4	$79.53	13.616%	$90.3588	$90.36	$90.35	$90.40
Purchase #5	$68.87	13.781%	$78.361	$78.36	$78.35	$78.40
Purchase #6	$231.25	13.671%	$262.8642	$262.86	$262.85	$262.90
Purchase #7	$171.89	10.407%	$189.7786	$189.78	$189.80	$189.80
7 purchase totals =	$822.68		$923.1686	$923.16	$923.10	$923.30