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	$249.33	12.406%	$280.2619	$280.26	$280.25	$280.30
Purchase #2	$179.98	12.720%	$202.8735	$202.87	$202.85	$202.90
Purchase #3	$75.65	11.623%	$84.4428	$84.44	$84.45	$84.40
Purchase #4	$239.80	3.756%	$248.8069	$248.81	$248.80	$248.80
Purchase #5	$135.60	10.808%	$150.2556	$150.26	$150.25	$150.30
Purchase #6	$81.78	9.753%	$89.756	$89.76	$89.75	$89.80
Purchase #7	$82.53	8.473%	$89.5228	$89.52	$89.50	$89.50
7 purchase totals =	$1,044.67		$1,145.9195	$1,145.92	$1,145.85	$1,146.00