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	$78.47	4.573%	$82.0584	$82.06	$82.05	$82.10
Purchase #2	$234.88	5.730%	$248.3386	$248.34	$248.35	$248.30
Purchase #3	$126.39	13.366%	$143.2833	$143.28	$143.30	$143.30
Purchase #4	$109.45	8.206%	$118.4315	$118.43	$118.45	$118.40
Purchase #5	$91.89	7.448%	$98.734	$98.73	$98.75	$98.70
Purchase #6	$157.97	5.300%	$166.3424	$166.34	$166.35	$166.30
Purchase #7	$245.73	9.421%	$268.8802	$268.88	$268.90	$268.90
7 purchase totals =	$1,044.78		$1,126.0684	$1,126.06	$1,126.15	$1,126.00