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	$91.69	9.578%	$100.4721	$100.47	$100.45	$100.50
Purchase #2	$236.27	4.566%	$247.0581	$247.06	$247.05	$247.10
Purchase #3	$63.31	7.598%	$68.1203	$68.12	$68.10	$68.10
Purchase #4	$48.62	8.664%	$52.8324	$52.83	$52.85	$52.80
Purchase #5	$115.44	13.596%	$131.1352	$131.14	$131.15	$131.10
Purchase #6	$133.31	5.492%	$140.6314	$140.63	$140.65	$140.60
Purchase #7	$247.66	13.404%	$280.8563	$280.86	$280.85	$280.90
7 purchase totals =	$936.30		$1,021.1058	$1,021.11	$1,021.10	$1,021.10