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	$245.36	13.536%	$278.5719	$278.57	$278.55	$278.60
Purchase #2	$79.82	4.291%	$83.2451	$83.25	$83.25	$83.20
Purchase #3	$150.91	9.220%	$164.8239	$164.82	$164.80	$164.80
Purchase #4	$37.52	9.414%	$41.0521	$41.05	$41.05	$41.10
Purchase #5	$108.54	7.595%	$116.7836	$116.78	$116.80	$116.80
Purchase #6	$85.43	5.262%	$89.9253	$89.93	$89.95	$89.90
Purchase #7	$229.74	13.808%	$261.4625	$261.46	$261.45	$261.50
7 purchase totals =	$937.32		$1,035.8644	$1,035.86	$1,035.85	$1,035.90