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	$116.32	13.118%	$131.5789	$131.58	$131.60	$131.60
Purchase #2	$232.49	7.165%	$249.1479	$249.15	$249.15	$249.10
Purchase #3	$48.86	7.570%	$52.5587	$52.56	$52.55	$52.60
Purchase #4	$125.42	12.819%	$141.4976	$141.50	$141.50	$141.50
Purchase #5	$48.85	7.715%	$52.6188	$52.62	$52.60	$52.60
Purchase #6	$73.93	12.800%	$83.393	$83.39	$83.40	$83.40
Purchase #7	$178.51	11.294%	$198.6709	$198.67	$198.65	$198.70
7 purchase totals =	$824.38		$909.4658	$909.47	$909.45	$909.50