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	$71.74	11.841%	$80.2347	$80.23	$80.25	$80.20
Purchase #2	$171.70	8.106%	$185.618	$185.62	$185.60	$185.60
Purchase #3	$207.52	8.516%	$225.1924	$225.19	$225.20	$225.20
Purchase #4	$245.26	11.114%	$272.5182	$272.52	$272.50	$272.50
Purchase #5	$102.69	6.424%	$109.2868	$109.29	$109.30	$109.30
Purchase #6	$45.34	13.509%	$51.465	$51.47	$51.45	$51.50
Purchase #7	$85.62	7.579%	$92.1091	$92.11	$92.10	$92.10
7 purchase totals =	$929.87		$1,016.4242	$1,016.43	$1,016.40	$1,016.40