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	$41.79	8.564%	$45.3689	$45.37	$45.35	$45.40
Purchase #2	$53.96	10.833%	$59.8055	$59.81	$59.80	$59.80
Purchase #3	$19.71	3.359%	$20.3721	$20.37	$20.35	$20.40
Purchase #4	$221.56	4.637%	$231.8337	$231.83	$231.85	$231.80
Purchase #5	$198.93	13.370%	$225.5269	$225.53	$225.55	$225.50
Purchase #6	$111.43	9.814%	$122.3657	$122.37	$122.35	$122.40
Purchase #7	$213.98	9.168%	$233.5977	$233.60	$233.60	$233.60
7 purchase totals =	$861.36		$938.8705	$938.88	$938.85	$938.90