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	$181.52	5.479%	$191.4655	$191.47	$191.45	$191.50
Purchase #2	$235.70	5.319%	$248.2369	$248.24	$248.25	$248.20
Purchase #3	$96.67	7.377%	$103.8013	$103.80	$103.80	$103.80
Purchase #4	$55.50	8.224%	$60.0643	$60.06	$60.05	$60.10
Purchase #5	$97.51	8.384%	$105.6852	$105.69	$105.70	$105.70
Purchase #6	$112.60	5.524%	$118.82	$118.82	$118.80	$118.80
Purchase #7	$82.86	3.516%	$85.7734	$85.77	$85.75	$85.80
7 purchase totals =	$862.36		$913.8466	$913.85	$913.80	$913.90