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	$65.90	8.203%	$71.3058	$71.31	$71.30	$71.30
Purchase #2	$57.96	13.380%	$65.715	$65.72	$65.70	$65.70
Purchase #3	$123.81	6.249%	$131.5469	$131.55	$131.55	$131.50
Purchase #4	$51.25	10.168%	$56.4611	$56.46	$56.45	$56.50
Purchase #5	$176.27	8.593%	$191.4169	$191.42	$191.40	$191.40
Purchase #6	$15.85	9.282%	$17.3212	$17.32	$17.30	$17.30
Purchase #7	$11.82	8.850%	$12.8661	$12.87	$12.85	$12.90
7 purchase totals =	$502.86		$546.6330	$546.65	$546.55	$546.60