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	$126.79	3.487%	$131.2112	$131.21	$131.20	$131.20
Purchase #2	$105.88	6.777%	$113.0555	$113.06	$113.05	$113.10
Purchase #3	$54.44	8.459%	$59.0451	$59.05	$59.05	$59.00
Purchase #4	$18.55	10.238%	$20.4491	$20.45	$20.45	$20.40
Purchase #5	$82.86	8.266%	$89.7092	$89.71	$89.70	$89.70
Purchase #6	$233.88	9.808%	$256.819	$256.82	$256.80	$256.80
Purchase #7	$47.51	3.151%	$49.007	$49.01	$49.00	$49.00
7 purchase totals =	$669.91		$719.2961	$719.31	$719.25	$719.20